ADEQUACY Of NASO.AN DATA TO DESCRIBE AREAL AND TEMPORAL VARIABILITY Of WATER QUALITY Of THE SAN JUAN RIVER DRAINAGE BASIN UPSTREAM FROM SHIPROCK, NEWMEXICO
By Carole L. Goetz and Cynthia G. Abeyta
U.S. GEOLOGICAL SURVEY
Water-Resources Investigations Report 85-4043
Albuquerque, New Mexico 1987 DEPARTMENT OF THE INTERIOR
DONALD PAUL HODEL, Secretary
U.S. GEOLOGICAL SURVEY
Dallas L. Peck, Director
For additional information Copies of this report can write to: be purchased from:
District Chief U.S. Geological Survey U.S. Geological Survey Water Resources Division Books and Open-File Reports Section Pinetree Office Park Federal Center 4501 Indian School Rd. NE, Suite 200 Box 25425 Albuquerque, New Mexico 87110 Denver, Colorado 80225 CONTENTS
Page
Abstract ...... 1
Introduction ...... 2
Description of the study area ...... 3
Population ...... 3 Water use ...... 3 Irrigated cropland ...... 3 Reservoirs ...... 7 Mineral production ...... 7 Geology ...... 7
Data used in this report ...... 9
Spatial variability of water quality ...... 13
Water-quality classification of streams ...... 14 Variability of concentrations or properties of selected water-quality constituents ...... 29 Variability of loads of selected water-quality constituents ..... 35 Box-and-whisker plots ...... 50
Temporal variability of water quality ...... 62
Seasonal Kendall test for trend magnitude ...... 62 Time-series plots ...... 66
Adequacy of NASQAN data to represent water quality throughout the basin ...... 77
Need for future study ...... 84
Summary of results ...... 85
Selected references ...... 89
111 FIGURES
Page
Figure 1. Map showing location of study area ...... 4
2. Graph showing population of study area ...... 5
3. Graph showing irrigated-cropland acreage in study area .... 5
4. Map showing location of irrigated agriculture, coal-mine and power-generation facilities, and metals mining ...... 6
5. Generalized geologic map
6. Map showing location o£ gaging stations and water-quality sampling sites ...... 12
7. Map showing predominant ions at selected gaging stations, October 1, 1973 - September 30, 1981 ...... 26
8-14. Maps showing variability of median:
8. Specific conductance, October 1, 1973 - September 30, 1981 ...... 31
9. Dissolved-sodium concentration, October 1, 1973 - September 30, 1981 ...... 32
10. Dissolved-sulfate concentration, October 1, 1973 - September 30, 1981 ...... 33
11. Dissolved-iron concentration, October 1, 1973 - September 30, 1981 ...... 34
12. Dissolved-manganese concentration, October 1, 1973 - September 30, 1981 ...... 36
13. Dissolved-orthophosphate phosphorus concentration, October 1, 1973 - September 30, 1981 ...... 37
14. Dissolved-radium-226 concentration, October 1, 1973 - September 30, 1981 ...... 38
IV FIGURES - Continued
Page
Figures 15-22. Maps showing the variability of the mean annual:
15. Product of specific conductance and streamflow, October 1, 1973 - September 30, 1981 ...... 42
16. Product of specific conductance and streamflow per square mile of drainage area, October 1, 1973 - September 30, 1981 ...... 43
17. Dissolved-sodium load, October 1, 1973 - September 30, 1981 ...... 44
18. Dissolved-sodium load per square mile of drainage area, October 1, 1973 - September 30, 1981 ...... 45
19. Dissolved-sulfate load, October 1, 1973 - September 30, 1981 ...... 46
20. Dissolved-sulfate load per square mile of drainage area, October 1, 1973 - September 30, 1981 ...... 47
21. Dissolved-radium-226 load, October 1, 1973 - September 30, 1981 ...... 48
22. Dissolved-radium-226 load per square mile of drainage area, October 1, 1973 - September 30, 1981 ...... 49
23-32. Graphs showing box-and-whisker plot of:
23. Streamflow data, October 1, 1973 - September 30, 1981 ...... 52
24. Dissolved-iron data, October 1, 1973 - September 30, 1981 ...... 53
25. Suspended-sediment-concentration data, October 1, 1973 - September 30, 1981 ...... 54
26. Dissolved-radium-226 data, October 1, 1973 - September 30, 1981 ...... 55
27. Specific-conductance data, October 1, 1973 - September 30, 1981 ...... 56
28. pH data, October 1, 1973 - September 30, 1981 ... 57 FIGURES - Continued
Page
Figures 23-32. Graphs showing box-and-whisker plot of: - Concluded
29. Dissolved-orthophosphate phosphorus data, October 1, 1973 - September 30, 1981 ...... 58
30. Dissolved-sodium data, October 1, 1973 - September 30, 1981 ...... 59
31. Dissolved-sulfate data, October 1, 1973 - September 30, 1981 ...... 60
32. Dissolved-manganese data, October 1, 1973 - September 30, 1981 ...... 61
33-43. Graphs showing time-series plots of:
33. pH and suspended-sediment concentration, October 1, 1973 - September 30, 1981, at Vallecito Creek near Bayfield, Colorado (station 09352900) ...... 67
34. Suspended-sediment concentration and specific conductance, October 1, 1973 - September 30, 1981, at San Juan River at Hammond Bridge near Bloomfield, New Mexico (station 09357100) ...... 67
35. Specific conductance, pH, dissolved- orthophosphate phosphorus concentration, and dissolved-sodium concentration, October 1, 1973 - September 30, 1981, at Animas River at Farmington, New Mexico (station 09364500) ..... 68
v, 36. Dissolved-sulfate, dissolved-iron, dissolved- manganese, and suspended-sediment concentrations, October 1, 1973 - September 30, 1981, at Animas River at Farmington, New Mexico (station 09364500) ..... 69
37. Dissolved-sulfate concentration, October 1, 1973 - September 30, 1981, at La Plata River at Colorado-New Mexico State line (station 09366500) ...... 70 FIGURES - Concluded
Page
Figures 33-43. Graphs showing time-series plots of: - Concluded
38. Specific conductance, pH, and dissolved-sodium, dissolved-sulfate, and dissolved-iron concentrations, October 1, 1973 - September 30, 1981, at Shumway Arroyo near Waterflow, New Mexico (station 09367561) ...... 71
39. Specific conductance and dissolved-sodium and dissolved-sulfate concentrations, October 1, 1973 - September 30, 1981, at Chaco River near Waterflow, New Mexico (station 09367950) ...... 72
40. Specific conductance, pH, and dissolved- orthophosphate phosphorus and dissolved- sodium concentrations, October 1, 1973 - September 30, 1981, at San Juan River at Shiprock, New Mexico (station 09368000) ...... 73
41. Dissolved-sulfate, dissolved-iron, dissolved- manganese, and suspended-sediment concentrations, October 1, 1973 - September 30, 1981, at San Juan River at Shiprock, New Mexico (station 09368000) ...... 74
42.--Specific conductance, pH, and dissolved-sodium concentration, October 1, 1973 - September 30, 1981, at San Juan River intake to Morgan Lake, New Mexico (station FC1) ...... 75
43.--Specific conductance and dissolved-sodium and dissolved-sulfate concentrations, October 1, 1973 - September 30, 1981, at Morgan Lake, New Mexico (station FC3) ...... 76
44. Map showing trends in water-quality parameters at selected U.S. Geological Survey stations and ability of the NASQAN stations to represent water quality at upstream stations ...... 79
TABLES
Table 1. Streamflow and water-quality stations used in this report ...... 10
2. Summary values for streamflow data in the drainage basin upstream from the San Juan River at Shiprock, New Mexico ...... 15
vii TABLES - Continued
Page
Table 3. Summary values for specific-conductance data in the drainage basin upstream from the San Juan River at Shiprock, New Mexico ...... 16
4. Summary values for pH data in the drainage basin upstream from the San Juan River at Shiprock, New Mexico ...... 18
5. Summary values for dissolved-orthophosphate phosphorus data in the drainage basin upstream from the San Juan River at Shiprock, New Mexico ...... 19
6. Summary values for dissolved-sodium data in the drainage basin upstream from the San Juan River at Shiprock, New Mexico ...... 20
7. Summary values for dissolved-sulfate data in the drainage basin upstream from the San Juan River at Shiprock, New Mexico ...... 21
8. Summary values for dissolved-iron data in the drainage basin upstream from the San Juan River at Shiprock, New Mexico ...... 22
9. Summary values for dissolved-manganese data in the drainage basin upstream from the San Juan River at Shiprock, New Mexico ...... 23
10. Summary values for dissolved-radium-226 data (radon method) in the drainage basin upstream from the San Juan River at Shiprock, New Mexico ...... 24
11. Summary values for suspended-sediment data in the drainage basin upstream from the San Juan River at Shiprock, New Mexico ...... 25
12. Water-quality classification of streams in the San Juan River basin upstream from Shiprock, New Mexico ...... 27
13. Percent contribution to the mean annual product of specific conductance and streamflow by subbasin for the San Juan River basin upstream from Shiprock, New Mexico ...... 41
14. Percent contribution to the mean annual dissolved- radium-226 load by subbasin for the San Juan River basin upstream from Shiprock, New Mexico ...... 41
vin TABLES - Concluded
Page
Table 15. Results of Seasonal Kendall test for trend magnitude 64
16. Trends detected and a criterion describing the adequacy of NASQAN stations to represent water quality at selected stations in the San Juan River basin upstream from Shiprock, New Mexico ...... 80
CONVERSION FACTORS
For readers who prefer to use International System (SI) units rather than the inch-pound units used in this report, the following conversion factors may be used.
Multiply inch-pound units Bv_ To obtain SI units
Length foot 0.3048 meter
Area square mile 2.590 square kilometer acre 0.004047 square kilometer
Flow cubic foot per second 0.02832 cubic meter per second
Mass ton 907.2 kilogram
Vo1ume acre-foot 1,233 cubic meter
IX ADEQUACY OF NASQAN DATA TO DESCRIBE AREAL AND TEMPORAL VARIABILITY
OF WATER QUALITY OF THE SAN JUAN RIVER DRAINAGE BASIN
UPSTREAM FROM SHIPROCK, NEW MEXICO
By Carole L. Goetz and Cynthia G. Abeyta
ABSTRACT
Analyses indicate that water quality in the San Juan River drainage basin upstream from Shiprock, New Mexico, is quite variable from station to station. Analyses are based on water-quality data from the U.S. Geological Survey WATSTORE files and the New Mexico Environmental Improvement Division's files.
In the northeastern part of the basin, most streams have calcium bicarbonate water. In the northwestern and southern part of the basin, the streams have calcium sulfate and sodium sulfate water. Geology, climate, land use, and water use affect water quality. Streamflow from snowmelt in high- mountain regions of the study area is largely calcium bicarbonate. Metals mining contributes sulfate to streamflow in parts of the basin. Irrigation- return flow contributes sodium to streamflow. Porous sandstones and interbedded shales in the southern part of the basin increase dissolved-solids concentration in runoff.
Based on box-and-whisker plots, dissolved-iron and suspended-sediment concentrations have the greatest temporal variability at individual sites. Areal variability from station to station also is great. Specific- conductance, pH, dissolved-orthophosphate phosphorus, dissolved-sodium, dissolved-sulfate, and dissolved-manganese data are next in variability. Dissolved-radium-226 data are the least variable. Water-quality variability is greatest at stations downstream from small flows from point-source discharges or stations located on ephemeral streams. Constituent concentrations frequently are large at these stations; the median specific conductance is 1,000 or more microsiemens per centimeter at 25 °Celsius. These stations have little influence on downstream water quality because of the low volumes of flow. A trend in one or more water-quality constituents for October 1, 1973, through September 30, 1981, was detected at 14 of 36 stations tested. Of those 14 stations, 5 are downstream from point-source discharges from power- generation facilities. At the upstream National Stream-Quality Accounting Network (NASQAN) station, Animas River at Farmington, New Mexico, 09364500, suspended-sediment concentration decreased 78 milligrams per liter per year. At the downstream NASQAN station, San Juan River at Shiprock, New Mexico, 09368000, no trends were found. At other upstream stations there were some increases and some decreases. The most consistent temporal trend in the basin was the decrease in pH at six stations.
The NASQAN stations, Animas River at Farmington and San Juan River at Shiprock, New Mexico, record large volumes of flow and represent an integration of the flow from many upstream tributaries. They do not represent what is occurring at specific points upstream in the basin; they provide accurate information on how water quality is changing over time at the station location. If a persistent change occurs upstream and involves a large volume of streamflow, it also will likely be detected at the downstream NASQAN stations at Farmington and Shiprock, New Mexico. A water-quality streamflow model would be necessary to accurately predict what is occurring simultaneously in the entire basin. Simultaneous sampling suitable for input into a model of water quality and streamflow in the San Juan River drainage basin upstream from Shiprock, New Mexico, needs to supplement the NASQAN data- collection program.
INTRODUCTION
The National Stream-Quality Accounting Network (NASQAN) was established in the early 1970's to describe the areal and temporal variability of water quality in the Nation's principal streams and to provide a data base for national and regional water-use planning. Accounting Unit 140801, upstream from Shiprock, New Mexico, was one of eight drainage basins chosen for evaluation of how well the data collected under the NASQAN program describe water-quality conditions and changes within the basin. Water-quality data at two NASQAN stations are compared to water-quality data available from 23 other surface-water stations within the basin.
The objectives of this study are as follows: (1) To describe, on both a spatial and temporal basis, the stream water quality throughout Accounting Unit 140801 upstream of the NASQAN station, 09368000, San Juan River at Shiprock; (2) to relate the water-quality variability to general causes, such as basin characteristics including land and water use; (3) to determine whether water-quality data collected at NASQAN station 09368000 and station 09364500, Animas River at Farmington, New Mexico, represent, on both a spatial and temporal basis, water quality at upstream stations; and (4) if water quality at NASQAN stations 09368000 and 09364500 does not represent upstream water quality, to describe the minimum data-collection program that might do so. DESCRIPTION OF THE STUDY AREA
The study area is the San Juan River drainage basin upstream from NASQAN station 09368000 located at Shiprock, New Mexico (fig. 1). The drainage basin upstream from the San Juan River at Shiprock includes approximately 12,900 square miles, a diverse area that includes deserts in New Mexico and 14,000- foot mountain peaks in Colorado. The drainage basin includes mountain, cobble streams in the north and ephemeral sand channels in the south. It is the second largest tributary of the Colorado River. A number of reservoirs are located in the drainage basin including the large Navajo Reservoir. Water from the San Juan River is used for agriculture, power generation, industrial and public supply, and recreation.
Population
Water use for public supplies and other cultural activities including agriculture, mining, and industries has increased with population growth in the basin. The San Juan River basin population trend is shown in figure 2. A review of population trends from 1860 through 1980 (U.S. Department of Commerce, 1860-1980) indicates that population fluctuated between 10,000 and 20,000 from 1860 until 1900. Population gradually increased from 32,000 to 46,000 between 1910 and 1950. Between the 1950 and the 1960 census, a population boom occurred, increasing the census count to more than 80,000 for both 1960 and 1970. The population remained stable between 1960 and 1970 but then increased dramatically in 1980. The 1980 census records a population of more than 120,000 in the San Juan River drainage basin above Shiprock, New Mexico.
Water Use
Agriculture has been, and currently is, the largest single use for water in the San Juan River basin. According to a report by the Colorado Water Conservation Board and U.S. Department of Agriculture (1974, p. IV-6 to IV-7), agricultural use accounted for nearly 93 percent of the total water depletion during 1965 and was projected to equal 77 percent of total depletion by 1980. Electric-power generation is the second largest water user, accounting for less than 4 percent of the total water depletion during 1965, but projected to equal 16 percent of total depletion by 1980.
Irrigated Cropland
Irrigated cropland in acres for the study area is given in figure 3 . A continual increase from 25,000 acres to nearly 160,000 acres of irrigated cropland occurred from 1889 to 1949 (U.S. Department of Commerce, 1860- 1980). Irrigated cropland decreased to 120,000 acres in 1959, then increased to 150,000 acres in 1969. Irrigated cropland has been decreasing since 1969 at a rate of about 1,400 acres per year. Most of the irrigated cropland is located along stream valleys (fig. 4). Streamflow from the San Juan River and its tributaries is the source of the irrigation water, which is supplied through a system of reservoirs and ditches. 108' 107° 38° V.OURAY/ -NH .SAGUACHE
< .COLORADO
GRANDE
'? o-" :V /PAGOSA nv V SPRINGS / I / f J \ ARCHULETA /\ 109° / y)
37° COLORADO NAVAJO NEW MEXIC RESERVOIR
RIO ARRIBA
SAN JUAN
SAN JUAN RIVER BASIN AND STUDY AREA MCKINLEY BOUNDARY
CROWNPOSNT SANDOVAL .D
40 KILOMETERS
EXPL.ANAT I ON
Ina^cRnnn, ~ | U.S. GEOLOGICAL SURVEY NASQAN GAGING STATION, |08J6BUUU| SAN JUAN R!VER AT SHIPROCK, NEW MEXICO
Figure 1.--Location of study area, IRRIGATED CROPLAND. IN ACRES U3 C C ~\ CD POPUUATI ON NJ 0) -M I O O I ~U O _l CD ~\ O T3 oo C CD C CTN 1 U3 D O CD QJ U) QJ 1 QJ rt C rt > C CD V^O Q. oo 0 1 Q. 0 -h O QJ rt O . rt o QJ -h IT "Q CD . i QJ O D C CD CL Q.
QJ C O
CD Q. QJ QJ U3 rt CD QJ rt
C Q. O O CD CD O Q. 3 3 CD -\ O O 3 CD CD C ~\ 00 CD QJ 3 o C O QJ I O rt - o 3 CD UD -h Q. OO CD O rt ~\ O CD 109° 108° 107*
I V.OURAY/ SAN HINSDALE SAGUACHE
A U.S. GEOLOGICAL SURVEY NASQAN GAGING STATION
MINERAL !Ri COAL-MINE AND POWER-GENERATION FACILITY GRANDE
SPRINGS Y
MONTEZUMA. ARCHULETA v_/
COLORADO NEW MEXIC
SAN JUAN
IVER BASIN BOUNDARY
SANDOVAL MCKINLEY
0 20 40 KILOMETERS Figure ^.--Location of irrigated agriculture, coal-mine and power-
generation facilities, and metals mining. Reservoirs
There are three large reservoirs in the study area that supply water for irrigation and provide recreation sites. These are Lemon Reservoir, Vallecito Reservoir, and Navajo Reservoir (fig. 4). Lemon Reservoir, the smallest of the three, is located on the Florida River, a tributary to the Animas River. Its capacity of 40,100 acre-feet is 1.4 times the mean annual flow of the Florida River entering the reservoir. It began impounding water in 1964. Vallecito Reservoir, located on the Los Pinos River, began impoundment in 1941. Its capacity of 120,300 acre-feet is 0.5 times the mean annual flow of the Los Pinos River entering the reservoir. The largest of the three, Navajo Reservoir, located on the San Juan River, began impoundment in 1963. Its capacity of 1,696,000 acre-feet is 2.2 times the mean annual flow of the San Juan River entering the reservoir. Release of water from these reservoirs is regulated through the dams and has changed the natural streamflow patterns at downstream sites.
Mineral Production
At present, income from mineral production in the basin far exceeds that obtained from agriculture, which was the primary source of income until about 1945 (Sorenson, 1967). Metals mining constituted an initial stimulus for the settlement of the northern part of the basin and continues to be important. By the mid-1940's oil and gas production became part of the economy throughout the basin.
In recent years, coal mining has become important, particularly in the western part of the basin, where strippable coal deposits cross the San Juan River, and in the south along the Chaco River drainage basin where extensive coal mining is planned. Two large, surface coal mines are located near and on opposite sides of the San Juan River as shown in figure 4. These two mines supply coal for electrical-power generation at a mine-mouth, electrical power-generation facility. The first mine began mining operations and electrical-power generation in 1963. Additional power-generation units were added in 1964, 1969, and 1970. The second mine began mining operations and power generation in 1973 with additional power-generation units added in 1976 and 1979. Coal production from these two mines increased from 2 million tons during 1964 to 11 million tons during 1981 (Nielsen, 1982).
Geology
Rocks in the San Juan River basin include Precambrian, Cambrian, Devonian, Mississippian, Pennsylvanian, Permian, Triassic, Jurassic, Cretaceous, Tertiary, and Quaternary rocks (Dane and Bachman, 1965; Tweto, 1979). Precambrian granitic and metamorphic rocks and Tertiary igneous rocks crop out along the northern section of the San Juan River's drainage basin where the headwaters of the Animas and Los Pinos Rivers emerge (fig. 5). The metamorphic rocks include slate, phyllite, gneiss, and schist. The volcanic rocks predominately are intermediate to felsic rocks, diabase, gabbro, andesite, breccia, tuff, conglomerate, and quartz latite. Headwaters of the dew Dj6o[O96 paz 3Jn6jj
SM313WOT
-IQ3S NVlUaWVD QNV 'NVINOA3Q --_-^_-_ NVIddlSSISSIW 'NVINVA1ASNN3d f^--TJT-
9C AyVlN3WIQ3S QNV 'A»VI1»31 '
:::::::::::::::s^!M'.7:::>r:::::::::::::::;' " " rr*«J*r--"--"
OdVHOlOD
80 J ,601 Piedra, San Juan, and Navajo Rivers emerge from the volcanic andesitic lava, breccia, tuff, and conglomerate. Igneous intrusive rocks of intermediate to felsic composition crop out near the northwest rim of the study area where the La Plata River emerges. Cambrian through Jurassic sedimentary rocks bound the Precambrian metamorphic and Tertiary volcanic rocks to the south. These sedimentary rocks consist mostly of quartzose and arkosic sandstone, shale, limestone, and some dolomite. The surface geology of the remainder of the basin, which includes the majority of the San Juan River valley and drainage area south of it, is composed primarily of Cretaceous and Tertiary sedimentary rocks and Quaternary alluvium. These sedimentary rocks consist mostly of interbedded sandstone and shale. The Quaternary alluvium is deposited along several of the stream channels.
DATA USED IN THIS REPORT
Two NASQAN stations are located upstream from Shiprock, New Mexico, and within Accounting Unit 140801. They are station 09368000, San Juan River at Shiprock, New Mexico, and station 09364500, Animas River at Farmington, New Mexico (fig. 6). These stations began operation as part of the NASQAN network on October 1, 1973, and April 4, 1979, respectively, continuing as NASQAN stations to the present. Because it was desired to analyze data collected through the NASQAN program, the period of record for data analysis is October 1, 1973, through September 30, 1981, a total of 8 years of record.
Additional streamflow and water-quality data used for this study include: (1) Streamflow and water-quality data collected and analyzed by the U.S. Geological Survey and maintained on its computerized Water Data Storage and Retrieval System (WATSTORE), and (2) self-monitoring, water-quality data for a mine-mouth power plant maintained on file by the New Mexico Environmental Improvement Division. A list of stations where data were collected is provided in table 1. Station locations are shown in figure 6.
Daily measurements of streamflow and some water-quality constituents were collected by the U.S. Geological Survey throughout the study area. Most water-quality constituents, however, are collected monthly or less frequently at U.S. Geological Survey stations. Records at some stations for some constituents were collected regularly from October 1, 1973, through September 30, 1981. Other stations have shorter or intermittent periods of record. Specific-conductance data were collected most frequently during water years 1974 through 1981 with daily records available for several stations. Data for major cations and anions, pH, and nutrients were collected fairly frequently, with monthly collection at selected stations. Metal and radiochemical data were collected less frequently with metals collected quarterly and radiochemicals collected semiannually at selected stations. Measurements of streamflow used in this report are daily means while measurements of water- quality constituents are instantaneous values.
The locations of the water-quality sites for the mine-mouth power plant are denoted as FC1 through FC6 in figure 6. These water-quality data were collected, analyzed, and computed as monthly mean values by the power- generation facility. Table 1. Streaaflow and water-quality stations used in this report
[Eight-digit station numbers are U.S. Geological Survey national station numbers; station numbers prefixed FC are stations operated by Four Corners Power Plant]
Station number Station name
09339900 East Fork San Juan River above Sand Creek, near Pagosa Springs, Colorado 09341200 Wolf Creek near Pagosa Springs, Colorado 09342500 San Juan River at Pagosa Springs, Colorado 09343000 Rio Blanco near Pagosa Springs, Colorado 09343300 Rio Blanco below Blanco Div. Dam, near Pagosa Springs, Colorado
09343400 Rio Blanco at U.S. Highway 84, near Pagosa Springs, Colorado 09344300 Navajo River above Chromo, Colorado 09344400 Navajo River below Oso Dam, near Chromo, Colorado 09346000 Navajo River above Edith, Colorado 09346400 San Juan River near Carracas, Colorado
09347200 Middle Fork Piedra River near Pagosa Springs, Colorado 09349800 Piedra River near Arboles, Colorado 09352900 Vallecito Creek near Bayfield, Colorado 09354500 Los Pinos River at La Boca, Colorado 09355000 Spring Creek at La Boca, Colorado
09355500 San Juan River near Archuleta, New Mexico 09356565 Canon Largo Wash near Blanco, New Mexico 09357000 San Juan River at Bloomfield, New Mexico 09357100 San Juan River at Hammond Bridge, near Bloomfield, New Mexico 09347205 Middle Fork Piedra River near Dyke, Colorado
09357250 Gallegos Canyon near Farmington, New Mexico 09357300 San Juan River above Animas River at Farmington, New Mexico 09357500 Animas River at Howardsville, Colorado 09358900 Mineral Creek above Silverton, Colorado 09361000 Hermosa Creek near Hermosa, Colorado
09361500 Animas River at Durango, Colorado 09363200 Florida River at Bondad, Colorado 09364500 Animas River at Farmington, New Mexico 09365000 San Juan River at Farmington, New Mexico 09366500 La Plata River at Colorado-New Mexico State line
10 Table 1. Streamflow and water-quality stations used in this report - Concluded
Station number Station name
09367500 La Plata River near Farmington, New Mexico 09367540 San Juan River near Fruitland, New Mexico FC1 San Juan River near Hogback, New Mexico 09367555 Shumway Arroyo near Fruitland, New Mexico 09367561 Shumway Arroyo near Waterflow, New Mexico
09367660 Chaco Wash near Star Lake Trading Post, New Mexico 09367680 Chaco Wash at Chaco Canyon National Monument, New Mexico 09367685 Ah-Shi-Sle-Pah Wash near Kimbeto, New Mexico 09367710 De-Na-Zin Wash near Bisti Trading Post, New Mexico 09367930 Hunter Wash at Bisti Trading Post, New Mexico
09367936 Burnham Wash near Burnham, New Mexico 09367938 Chaco River near Burnham, New Mexico FC2 Chaco River upstream of power plant FC3 Morgan Lake FC4 Ash Pond Effluent
FC5 Chaco River downstream of power plant 09367950 Chaco River near Waterflow, New Mexico 09368000 San Juan River at Shiprock, New Mexico FC6 San Juan River at Shiprock, New Mexico
11 109° 108" 107*
SAN ) HINSDALE
|09368000| Ml GUEL U.S. GEOLOGICAL SURVEY GAGING STATION AND NUMBER--Box around number indicates a NASQAN stat ion
GRANDE
MONTEZUMA.
09367540 COLORADO
RCHULETA V 09i56565
?IVER BASIN BOUNDARY
0 20 40 KILOMETERS Figure 6.--Location of gaging stations and water-quality sampling sites
12 SPATIAL VARIABILITY OF WATER QUALITY
Spatial variation, as used in this report, is the variation in water quality from station to station throughout the basin. Statistics used to summarize the variability of water-quality data collected at 40 stations throughout the study area are: (1) the number of measurements, (2) the date of the first measurement, (3) the date of the last measurement, (4) the mean, (5) the median, (6) the mode, (7) the minimum, and (8) the maximum. Both the mean and the median are measures of central tendency. The median, being the midpoint of the measurements if arranged in order by numerical value, is not affected by extreme values. The mean, being the sum of the measurements divided by the number of measurements, can be greatly affected by extreme values. The mode is the value occurring most frequently in a group of measurements. It represents the condition found most often at a measurement site.
Summary values for streamflow data are given in table 2. Daily values for streamflow data are analyzed rather than instantaneous streamflow data because the larger amount of data in the daily-values file is more representative of the true population. Statistics for values of specific conductance and pH and concentrations of dissolved-orthophosphate phosphorus, dissolved sodium, dissolved sulfate, dissolved iron, dissolved manganese, dissolved radium-226, and suspended sediment are given in tables 3, 4, 5, 6, 7, 8, 9, 10 and 11, respectively.
Dissolved-orthophosphate phosphorus, dissolved-iron and dissolved- manganese data required special treatment because these data are often reported as "less than" the lower limit of detection. An approach was taken to use the many "less than" values that appear in the data, and a simplistic evaluation of the "less than" data was made. If a value is given as less than 10 micrograms per liter, for example, it is known to be between 0 and 10 micrograms per liter. Therefore, the midpoint of the known range was chosen, 5 micrograms per liter, and that midpoint value was used in the calculation of means, medians, modes, minimums and maximums. It is felt that this evaluation of "less than" values introduces the least amount of bias into the data set. To delete the "less than" values from the data set would bias the statistics toward the higher end of the scale. To evaluate the less than 10 values as either 0 or 10 would bias these values toward one end or the other of the known range.
The pH data presented a problem in the calculation of the mean because of the logarithmic scale for pH measurement. Mean values for pH have been omitted.
13 Streamflow and specific-conductance values, dissolved-sodium, dissolved- sulfate, dissolved-iron, dissolved-tnanganese, and suspended-sediment concentrations are all highly variable throughout the study area. For example, the ranges of the above-named constituents are: 0.00 through 13,700 cubic feet per second (table 2) for streamflow; 30 through 16,300 microsiemens per centimeter (table 3) for specific conductance; 0.1 through 3,700 milligrams per liter (table 6) for dissolved sodium; 1.7 through 8,300 milligrams per liter (table 7) for dissolved sulfate; 0 through 21,000 micrograms per liter (table 8) for dissolved iron; 0 through 8,800 microgratns per liter (table 9) for dissolved manganese; and 0 through 966,000 milligrams per liter (table 11) for suspended sediment. Concentrations of dissolved- orthophosphate phosphorus and dissolved radium-226 are much more uniform over the basin. For example, the ranges of these constituents are: 0.00 through 2.6 milligrams per liter (table 5) for dissolved-orthophosphate phosphorous, and 0.02 through 0.56 picocurie per liter (table 10) for dissolved radium- 226. Considering the logarithmic scale for pH (hydrogen-ion concentration), the variation of 2.4 through 10.4 units (table 4) is very large.
Water-Quality Classification of Streams
The generalized water-quality classification of streams in the San Juan River basin is shown in figure 7. Chemical symbols indicate the water-quality classification at the station 50 percent or more of the time. A detailed accounting of the water-quality classification at each station is given in table 12. A station is included if it had three or more analyses and the cation and anion sums were equal or balanced to within 5 percent of each other. The waters were classified according to the predominant cation and anion. If a cation or anion made up 50 percent or more of the milliequivalents, it was considered the predominant ion. If no one cation or anion made up 50 percent of the milliequivalents, a second cation or anion was then added so that 50 percent or more of the milliequivalents were accounted for, making the water a three or more ionic-composition water.
Most streams in the northeastern part of the basin have calcium bicarbonate water (fig. 7). Streams in the northwestern and western part of the basin have calcium sulfate and sodium sulfate water. The calcium bicarbonate streams in the northeastern part of the basin flow through igneous and sedimentary rocks (fig. 5) and over densely vegetated terrain. Rocks in the southern part of the basin are entirely sedimentary and consist mainly of easily eroded sandstones and shales. Vegetation is sparse. Due to the lower latitude and altitude, much less of the precipitation is in the form of snow and precipitation falls less frequently than in the northern basin. More of the runoff- saturates through the porous and easily eroded soils and reflects cation and anion concentrations related to the rock types.
14 Table 2. Summary values for streamflov data in the drainage basin upstream from the San Juan River at Siiprock, New Mexico
[Mean, median, mode, minimum, and maximum values are given in cubic feet per second]
Station Number of Date of first Date of last number measurements measurement measurement Mean Median Mode Minimum Maximum
09339900 2,557 73-10-01 80-09-30 85 20 10 5.0 1,020 09341200 730 73-10-01 75-09-30 31 5.0 1.9 1.5 348 09342500 2,557 73-10-01 80-09-30 371 80 46 14 4,220 09343300 2,922 73-10-01 81-09-30 30 21 21 1.0 602 09346000 2,922 73-10-01 81-09-30 60 43 32 8.0 435 09346400 2,922 73-10-01 81-09-30 543 179 110 28 5,610 09347200 730 73-10-01 75-09-30 42 12 12 3.5 429 09347205 1,461 77-10-01 81-09-30 53 11 6.0 2.0 568 09349800 2,922 73-10-01 81-09-30 387 99 60 25 4,630 09352900 2,922 73-10-01 81-09-30 132 38 14 6.7 1,240 09354500 2,922 73-10-01 81-09-30 241 111 70 6.1 2,110 09355000 2,922 73-10-01 81-09-30 32 20 67 1.8 329 09355500 2,922 73-10-01 81-09-30 1,160 742 480 246 5,480 09356565 1,461 77-10-01 81-09-30 17 .01 .00 .00 1,380 09357100 1,461 77-10-01 81-09-30 1,250 735 1,780 130 5,390 09357250 1,461 77-10-01 81-09-30 .75 .00 .00 .00 150 09357500 2,922 73-10-01 81-09-30 89 22 14 10 923 09358900 730 73-10-01 75-09-30 20 4.7 1.8 1.5 180 09361000 2,557 73-10-01 80-09-30 130 25 17 7.0 1,880 09361500 2,922 73-10-01 81-09-30 735 258 180 129 7,550 09363200 2,922 73-10-01 81-09-30 72 35 30 5.2 855 09364500 2,922 73-10-01 81-09-30 793 282 220 5.3 8,060 09366500 2,922 73-10-01 81-09-30 39 8.0 10 .00 1,080 09367500 2,922 73-10-01 81-09-30 33 2.0 .00 .00 1,260 09367540 1,096 77-10-01 80-09-30 2,540 1,400 2,120 270 13,700 09367555 2,465 75-01-01 81-09-30 .56 .00 .00 .00 254 09367561 2,576 74-09-12 81-09-30 2.2 1.4 2.0 .00 320 09367660 1,461 77-10-01 81-09-30 .83 .00 .00 .00 61 09367680 2,002 76-04-08 81-09-30 5.0 .00 .00 .00 606 09367685 1,658 77-03-18 81-09-30 1.2 .00 .00 .00 133 09367710 2,100 76-01-01 81-09-30 4.6 .00 .00 .00 657 09367930 2,387 75-03-20 81-09-30 .83 .00 .00 .00 168 09367936 1,461 77-10-01 81-09-30 .29 .00 .00 .00 71 09367938 1,461 77-10-01 81-09-30 28 .00 .00 .00 3,900 09367950 2,161 75-11-01 81-09-30 37 17 20 .00 2,330 09368000 2,922 73-10-01 81-09-30 1,850 1,230 1,200 76 13,700
15 Table 3. Summary values for specific-tMnductance data in the drainage basin up- stream from the San Juan River at Shlprock, New Mexico
[Mean, median, mode, minimum, and maximun values are given in microsiemens per centimeter at 25 degrees Celsius]
Station Number of Date of first Date of last number measurements measurement measurement Mean Median Mode Minimum Maximum
09339900 46 76-10-04 81-08-31 131 130 130 70 180 09341200 18 74-03-26 75-08-25 48 50 34 30 80 09342500 63 76-10-05 81-08-31 161 140 140 60 430 09343000 13 74-04-16 74-10-02 124 131 175 69 175 09343300 36 74-04-16 75-07-10 111 106 98 68 184 09344300 16 74-04-16 74-10-02 142 152 78 78 193 09346000 76 73-11-26 81-08-31 259 240 240 112 900 09346400 22 80-01-02 81-09-01 315 290 290 100 800 09347200 17 74-03-27 75-08-04 60 62 44 43 80 09347205 42 77-10-11 81-08-31 71 70 70 50 120 09349800 24 80-01-02 81-09-01 324 325 130 110 560 09352900 98 73-10-04 81-08-26 75 75 70 36 120 09354500 22 74-05-03 81-08-25 288 245 180 160 950 09355000 22 74-05-03 81-08-25 643 400 270 260 1,400 09355500 67 73-10-29 81-06-26 282 280 280 180 480 09356565 44 77-12-16 81-09-09 3,350 1,900 1,500 770 .11,200 09357100 48 77-12-09 81-09-08 424 409 507 250 940 09357250 15 78-02-03 81-07-26 1,650 1,750 390 390 2,850 09357300 71 73-10-30 79-09-25 495 489 365 282 1,800 09357500 18 74-04-03 75-08-27 224 198 156 105 358 09358900 18 74-04-03 75-08-27 242 198 60 60 529 09361000 49 76-10-29 80-08-29 563 600 750 180 1,200 09361500 66 75-06-08 81-08-19 486 500 680 100 1,000 09363200 61 76-10-29 81-08-25 478 450 380 260 1,200 09364500 81 73-10-30 81-08-27 680 750 800 205 1,120 09365000 246 73-10-01 81-08-27 512 490 440 210 2,050 09366500 46 77-11-29 81-08-24 1,220 1,250 1,210 336 2,000
16 Table 3. Summary values for specific-conductance data in the drainage basin up- stream from the San Juan River at Shiprock, New Mexico - Concluded
Station Nunber of Date of first Date of last number measurements measurement measurement Mean Median Mode Minimum Maximum
09367500 43 77-12-12 81-08-28 2,370 2,200 2,000 517 4,850 09367540 47 77-12-14 81-09-08 505 462 450 250 965 09367555 8 76-07-26 78-10-24 793 850 480 480 950 09367561 216 74-08-13 81-09-03 6,740 6,570 6,000 500 16,300 09367660 65 77-11-07 81-09-16 583 393 320 102 6,700 09367680 105 76-08-06 81-07-01 464 440 420 185 900 09367685 70 77-07-18 81-09-30 829 698 800 280 2,600 09367710 46 74-08-12 81-07-13 721 686 700 220 1,500 09367930 86 74-10-31 81-09-23 1,060 981 1,000 435 5,010 09367936 20 77-11-06 81-09-23 793 711 690 520 1,420 09367938 36 77-07-20 81-07-02 1,180 812 700 300 8,400 09367950 150 75-11-13 81-09-03 1,950 1,800 2,000 310 10,900 09368000 220 73-10-01 81-09-01 675 638 550 265 2,450 FC1 74 74-01-15 80-10-15 514 506 615 234 709 FC2 13 74-08-15 79-11-15 1,630 946 610 610 6,560 FC3 77 73-10-15 80-10-15 1,510 1,550 1,050 980 1,920 PC* 65 74-01-15 80-10-15 3,350 3,190 3,090 2,040 11,800 FC5 70 73-10-15 80-10-15 2,410 2,140 980 980 8,000 FC6 71 74-04-15 80-10-15 616 590 278 278 1,100
17 Table 4. Suamary values for pH data in the drainage basin upstream from the San Juan River at Shiprock, New Mexico
[Median, mode, minimum, and maximum values are given in standard units]
Station Number of Date of first Date of last number measurements measurement measurement Median Mode Minimum Maximum
09341200 18 74-03-26 75-08-25 8.1 8.5 7.3 8.6 09343000 4 74-04-23 74-07-03 7.8 7.8 7.7 8.1 09343300 4 74-04-23 74-07-03 7.8 7.8 7.7 8.1 09344300 4 74-04-23 74-07-03 7.8 7.5 7.5 8.0 09346000 10 73-11-26 74-09-19 8.0 8.0 7.8 8.8 09347200 18 74-03-27 75-08-25 8.2 8.3 7.3 8.8 09352900 95 73-10-04 81-08-26 7.8 7.8 6.4 8.6 09355500 67 73-10-29 81-06-26 8.2 8.2 7.2 9.5 09356565 44 77-12-16 81-09-09 8.0 8.4 6.8 8.7 09357100 48 77-12-09 81-09-08 8.3 8.1 7.6 8.9 09357250 15 78-02-03 81-07-26 8.5 8.5 6.9 9.1 09357300 70 73-10-30 79-09-25 8.2 8.0 7.3 9.0 09357500 17 74-04-03 75-08-27 7.7 7.2 7.2 8.3 09358900 16 74-04-03 75-08-27 7.8 7.6 5.8 8.5 09364500 81 73-10-30 81-08-27 8.2 8.3 7.7 8.9 09365000 237 73-10-01 81-08-27 8.0 7.8 7.1 8.9 09366500 46 77-11-29 81-08-24 8.1 7.9 7.1 9.1 09367500 43 77-12-12 81-08-28 8.3 8.2 7.8 8.6 09367540 47 77-12-14 81-09-08 8.2 8.0 7.8 8.8 09367555 8 76-07-26 78-10-24 7.2 7.1 7.0 7.6 09367561 186 74-08-13 81-09-03 7.4 7.2 2.4 10.4 09367660 65 77-11-07 81-09-16 7.5 7.2 7.0 8.8 09367680 103 76-08-06 81-07-01 7.5 7.5 6.3 8.5 09367685 70 77-07-18 81-09-30 7.6 7.3 6.6 8.5 09367710 39 74-08-12 81-07-13 7.8 7.6 6.5 8.5 09367930 74 75-07-11 81-09-23 7.7 7.6 6.8 9.8 09367936 20 77-11-06 81-09-23 8.1 8.1 7.3 9.3 09367938 36 77-07-20 81-07-02 8.3 8.3 6.7 8.9 09367950 148 75-11-13 81-09-03 7.7 7.3 6.8 8.6 09368000 195 73-10-01 81-09-01 8.1 8.0 7.0 9.0 PCI 74 74-01-15 80-10-15 8.2 8.0 7.4 8.7 FC2 13 74-08-15 79-11-15 8.2 7.9 7.9 8.4 FC3 77 73-10-15 80-10-15 8.4 8.4 4.5 8.8 PC* 65 74-01-15 80-10-15 8.3 8.4 6.6 9.2 FC5 70 73-10-15 80-10-15 8.3 8.3 7.7 8.8 FC6 71 74-04-15 80-10-15 8.3 8.3 7.8 8.7
18 Table 5. Sunmary values for dissolved-orthophosphate phosphorus data in the drainage basin upstream from the San Juan River at Shiprock, New Mexico
[Mean, median, mode, minimum, and maximum values are given in milligrams per liter]
Station Number of Date of first Date of last number measurements measurement measurement Mean Median Mode Minimum Maximum
09341200 18 74-03-26 75-08-25 0.03 0.02 0.02 0.01 0.10 09343000 7 74-04-23 74-09-19 .04 .04 .03 .03 .06 09343300 7 74-04-23 74-09-19 .03 .03 .03 .01 .05 09344300 7 74-04-23 74-09-19 .23 .05 .05 .02 1.2 09346000, 10 73-11-26 74-09-19 .05 .05 .05 .02 .08 09347200 18 74-03-27 75-08-25 .04 .04 .03 .01 .06 09352900 64 73-10-04 80-10-08 .05 .01 .01 .00 2.6 09355500 67 73-10-29 81-06-26 .02 .01 .01 .00 .24 09357300 48 74-09-26 79-09-25 .01 .01 .01 .01 .05 09357500 18 74-04-03 75-08-27 .01 .01 .01 .01 .12 09358900 18 74-04-03 75-08-27 .01 .01 .01 .01 .03 09364500 74 73-10-30 80-09-03 .02 .01 .01 .00 .08 09365000 72 73-10-30 81-08-27 .04 .03 .01 .01 .18 09367561 59 74-08-13 80-09-02 .15 .08 .04 .01 1.0 09367680 29 76-08-06 80-02-15 .06 .06 .06 .01 .16 09367710 8 74-08-12 78-11-15 .06 .06 .06 .01 .12 09367930 11 76-05-07 78-11-15 .05 .04 .04 .02 .13 09367950 35 75-11-13 80-08-05 .02 .01 .01 .00 .09 09368000 131 73-10-30 80-09-29 .03 .03 .02 .00 .20
19 Table 6. Summary values for dissolved-sodiun data in the drainage basin upstream from the j»an Juan River at Shiprock, New Mexico
[Mean, median, mode, minimum, and raaximun values are given in milligrams per liter]
Station Number of Date of first Date of last number measurements measurement measurement Mean Median Mode Minimum Maximum
09341200 18 74-03-26 75-08-25 2.9 2.6 2.1 1.7 5.5 09343000 7 74-04-23 74-09-19 6.5 6.6 3.5 3.5 8.5 09343300 7 74-04-23 74-09-19 6.7 6.9 6.9 3.6 9.1 09344300 7 74-04-23 74-09-19 5.5 5.4 3.3 3.3 7.6 09346000 10 73-11-26 74-09-19 9.8 9.9 8.1 6.5 12 09347200 18 74-03-27 75-08-25 3.8 3.8 2.6 2.3 5.5 09352900 99 73-10-04 81-08-26 1.3 1.1 1.1 0.1 3.5 09355500 67 73-10-29 81-06-26 15 14 14 8.3 24 09356565 23 77-12-16 81-09-09 1,000 770 1,700 160 2,800 09357100 45 77-12-09 81-09-08 35 31 20 14 120 09357250 14 78-02-03 81-07-02 320 360 390 89 540 09357300 71 73-10-30 79-09-25 42 39 24 14 270 09357500 18 74-04-03 75-08-27 1.9 1.8 1.2 1.0 3.3 09358900 18 74-04-03 75-08-27 2.8 2.0 1.1 0.9 6.0 09364500 80 73-10-30 81-08-27 35 40 46 5.0 75 09365000 243 73-10-01 81-08-27 40 36 39 7.2 300 09366500 45 77-11-29 81-08-24 52 58 48 11 76 09367500 40 77-12-12 81-08-28 270 220 160 23 700 09367540 46 77-12-14 81-09-08 38 32 26 9.5 130 09367561 83 74-08-13 81-09-03 1,300 1 ,300 1,300 160 3,700 09367660 6 78-05-08 81-03-04 67 64 44 44 100 09367680 33 76-08-06 81-07-01 82 85 62 37 150 09367685 5 78-02-08 81-03-16 140 130 130 98 180 09367710 14 74-08-12 81-07-13 140 140 130 95 200 09367930 22 75-07-11 81-03-11 180 180 110 91 340 09367936 4 78-05-02 80-09-10 150 150 140 140 170 09367938 18 78-02-07 81-07-02 130 140 130 34 250 09367950 50 75-11-13 81-09-03 240 240 230 130 710 09368000 218 73-10-01 81-09-01 56 49 40 12 240 FC1 21 78-10-15 80-10-15 38 30 20 9.5 90 FC3 21 78-10-15 80-10-15 140 140 170 97 190 P& 15 78-10-15 79-12-15 270 260 180 50 600
20 Table 7. Sumnary values for dissolved-sulfate data in the drainage basin upstream from the San Juan River at Shiprock, New Mexico
[Mean, median, mode, minimun, and maximum values are given in milligrams per liter]
Station Number of Date of first Date of last number measurements measurement measurement Mean Median Mode Minimun Maximum
09341200 18 74-03-26 75-08-25 4.7 4.3 4.6 2.6 7.6 09343000 7 74-04-23 74-09-19 6.5 6.1 5.0 5.0 8.9 09343300 7 74-04-23 74-09-19 6.5 6.6 5.1 5.1 8.9 09344300 7 74-04-23 74-09-19 28 33 14 14 36 09346000 10 73-11-26 74-09-19 45 45 27 27 59 09347200 18 74-03-27 75-08-25 5.4 5.2 4.8 3.2 7.3 09352900 98 73-10-04 81-08-26 9.8 9.0 12 1.7 36 09355500 67 73-10-29 81-06-26 52 50 47 27 100 09356565 22 77-12-16 81-09-09 2,400 1,900 3,600 300 6,000 09357100 44 77-12-09 81-09-08 110 110 120 50 320 09357250 14 78-02-03 81-07-02 580 580 65 65 1,300 09357300 71 73-10-30 79-09-25 140 130 160 48 700 09357500 18 74-04-03 75-08-27 75 68 130 33 130 09358900 18 74-04-03 75-08-27 100 78 120 25 250 09364500 80 73-10-30 81-08-27 180 200 220 36 390 09365000 243 73-10-01 81-08-27 140 130 150 44 770 09366500 45 77-11-29 81-08-24 500 540 610 82 820 09367500 40 77-12-12 81 -08-28 1,000 860 160 160 2,500 09367540 46 77-12-14 81-09-08 140 120 120 50 400 09367561 83 74-08-13 81-09-03 3,800 3,800 3,400 390 8,300 09367660 6 78-05-08 81-03-04 71 74 4.7 4.7 130 09367680 34 76-08-06 81-07-01 71 58 57 30 200 09367685 5 78-02-08 81-03-16 180 180 100 100 250 09367710 13 74-08-12 81-07-13 140 140 150 80 200 09367930 22 75-07-11 81-03-11 280 220 110 52 710 09367936 4 78-05-02 80-09-10 170 200 21 21 280 09367938 19 78-02-07 81-07-02 150 150 180 74 300 09367950 49 75-11-13 81-09-03 900 870 1,200 240 2,800 09368000 218 73-10-01 81-09-01 210 190 130 58 1,100 FC1 74 74-01-15 80-10-15 150 160 170 50 280 FC2 10 74-08-15 79-04-15 820 370 70 70 3,400 FC3 77 73-10-15 80-10-15 560 560 570 350 850 FG4 65 74-01-15 80-10-15 1,900 1,900 1,600 1,100 2,600 FC5 70 73-10-15 80-10-15 1,300 1,100 450 360 5,000 FC6 71 74-04-15 80-10-15 190 190 120 58 450
21 Table 8. Summary values for dissolved-iron data in the drainage basin upstream from the San Juan River at Shiprock, New Mexico
[Mean, median, mode, minimum, and maximum values are given in micrograms per liter]
Station Number of Date of first Date of last number measurements measurement measurement Mean Msdian Mode Minimum Maximum
09341200 17 74-03-26 75-08-25 50 40 30 10 120 09343000 7 74-04-23 74-09-19 20 20 20 10 50 09343300 7 74-04-23 74-09-19 20 20 20 10 50 09344300 7 74-04-23 74-09-19 50 20 20 20 200 09346000 10 73-11-26 74-09-19 30 20 20 10 50 09347200 17 74-03-27 75-08-25 60 50 40 20 140 09352900 56 73-10-04 81-05-27 30 20 20 10 340 09355500 67 73-10-29 81-06-26 10 10 10 10 50 09356565 27 77-12-16 81-09-09 110 40 40 10 970 09357100 45 77-12-09 81-09-08 30 20 20 10 280 09357250 15 78-02-03 81-07-26 160 80 40 10 780 09357300 48 74-09-26 79-09-25 20 20 10 0 210 09357500 18 74-04-03 75-08-27 40 30 20 10 80 09358900 18 74-04-03 75-08-27 170 80 50 20 520 09364500 78 73-10-30 81-08-27 20 10 10 10 160 09365000 137 73-10-30 81-08-27 40 10 10 10 1,400 09366500 45 77-11-29 81-08-24 40 20 20 10 450 09367500 40 77-12-12 81-08-28 40 30 30 10 340 09367540 46 77-12-14 81-09-08 40 20 20 10 320 09367561 82 74-08-13 81-09-03 680 30 30 10 16,000 09367660 6 78-05-08 81-03-04 370 290 120 120 1,000 09367680 64 76-08-06 81-07-01 540 80 40 10 21,000 09367685 15 78-01-12 81-04-15 730 410 30 30 2,600 09367710 18 74-08-12 81-07-13 370 260 80 20 1,400 09367930 23 76-01-29 81-03-11 1,300 60 40 10 16,000 09367936 4 78-05-02 80-09-10 550 200 100 100 1,700 09367938 19 78-02-07 81-07-02 430 200 60 10 2,200 09367950 71 75-11-13 81-09-03 30 20 10 0 340 09368000 153 73-10-30 81-09-01 20 10 10 10 710
22 upstream from the San Juan River at Shiprock, New Mexico
[Mean, median, node, minimum, and maximum values are given in micrograms per liter]
Station Number of Date of first Date of last number measurements measurement measurement Maan Median Mode Minimun Maximum
09341200 18 74-03-26 75-08-25 6 10 10 5 20 09347200 18 74-03-27 75-08-25 5 10 10 5 10 09352900 55 73-10-04 81-05-27 9 10 10 2 50 09355500 23 73-10-29 81-06-26 7 10 10 2 30 09356565 11 78-05-02 81-09-09 1,200 180 10 0 4,400 09357100 24 77-12-09 81-09-08 17 10 10 4 52 09357250 5 79-08-10 81-07-26 430 10 10 0 2,100 09357500 18 74-04-03 75-08-27 360 300 280 130 850 09358900 18 74-04-03 75-08-27 360 340 630 70 630 09364500 23 73-10-30 81-08-27 51 40 10 10 180 09365000 15 74-04-02 81-05-05 21 10 10 0 70 09366500 15 77-11-29 81-08-24 31 13 10 2 110 09367500 20 77-12-12 81-08-28 250 200 20 0 960 09367540 24 77-12-14 81-09-08 16 10 10 4 90 09367561 60 74-12-18 81-09-03 480 440 10 3 2,800 09367680 44 77-02-12 81-07-01 230 10 10 0 8,800 09367685 13 78-01-12 81-04-15 21 10 10 0 80 09367710 11 76-07-13 81-07-13 5 10 10 0 10 09367930 12 76-08-19 81-03-11 83 10 10 0 930 09367938 8 78-05-08 81-07-02 11 10 20 2 20 09367950 49 75-12-11 81-09-03 12 10 10 0 90 09368000 31 74-09-26 81-09-01 80 7 10 4 2,100 FC1 65 74-02-15 80-10-15 0 0 0 0 6 FC3 59 73-10-15 80-10-15 0 0 0 0 0 F<& 59 74-01-15 79-12-15 1 0 0 0 4
23 Table 10. Summary values for dissolved-radiim-226 data (radon method) in the drainage basin upstream from titejian Juan River at Shiprock, Mew Mexico
[Mean, median, tnode, minimum, and maximum values are given in picocuries per liter]
Station Number of Date of first Date of last number measurements measurement measurement Mean Median Mode Minimum Maximum
09352900 9 73-10-04 81-05-27 0.06 0.06 0.06 0.04 0.11 09355500 7 78-02-21 81-04-06 0.11 0.09 0.05 0.05 0.22 09364500 8 73-10-30 80-09-30 0.09 0.08 0.08 0.07 0.14 09365000 3 79-11-29 81-04-08 0.06 0.06 0.05 0.05 0.07 09367561 12 74-12-18 81-08-04 0.12 0.10 0.07 0.03 0.26 09367680 11 77-02-14 80-02-15 0.14 0.08 0.06 0.02 0.56 09367950 12 77-11-29 81-07-10 0.12 0.10 0.10 0.04 0.18 09368000 16 73-10-30 81-05-06 0.08 0.08 0.06 0.03 0.11
24 Table 11. Summary values for suspended-sediment data in the drainage basin upstream CiXni the San Juan River at Shiprock, New Mexico
[Mean, median, mode, minimum, and maximum values are given in milligrams per liter]
Station Number of Date of first Date of last number measurements measurement measurement Mean Median Mode Minimum Maximum
09341200 18 74-03-26 75-08-25 23 8 4 1 185 09343000 12 74-04-16 74-10-02 16 10 3 2 59 09343300 35 74-04-16 75-07-10 904 165 13 2 5,540 09344300 15 74-04-16 74-10-02 41 11 14 2 168 09346000 17 73-11-26 74-10-02 576 44 32 4 4,830 09347200 16 74-03-27 75-08-25 10 4 4 0 63 09352900 82 73-10-04 81-08-26 4 2 1 0 35 09355500 7 77-04-27 81-06-26 9 7 4 4 16 09356565 47 77-12-16 81-09-09 97,300 37,400 42 42 525,000 09357100 67 77-12-09 81-09-21 1,900 383 38 29 44,100 09357250 18 78-02-03 81-07-26 34,600 16,400 1,460 46 123,000 09357500 18 74-04-03 75-08-27 18 4 2 0 229 09358900 18 74-04-03 75-08-27 16 10 6 2 60 09364500 102 74-01-01 81-07-15 2,140 934 34 8 16,700 09365000 19 77-04-27 81-08-27 442 275 36 36 1,450 09366500 41 77-11-29 81-08-24 355 32 8 3 4,780 09367500 54 77-12-12 81-06-29 3,690 728 21 21 35,100 09367540 65 77-12-14 81-09-21 2,490 539 38 25 58,200 09367555 9 76-07-26 78-10-24 224,000 92,700 298 298 966,000 09367561 275 74-10-24 81-09-21 13,800 789 30,900 15 534,000 09367660 70 77-11-07 81-09-16 17,700 15,200 14,800 706 106,000 09367680 587 76-08-06 81-09-18 29,700 23,400 21 ,400 395 147,000 09367685 109 77-07-18 81-09-30 51,600 50,200 52,500 6,000 220,000 09367710 84 75-07-10 81-07-13 57,000 36,100 10,600 1,410 197,000 09367930 162 74-09-11 81-09-23 55,300 28,800 28,800 2,420 280,000 09367936 22 77-11-06 81-09-23 106,000 75,100 23,900 23,900 559,000 09367938 42 77-07-20 81-07-02 58,800 49,600 2,470 2,470 236,000 09367950 249 75-11-13 81-09-21 40,000 36,700 49,400 3 280,000 09368000 143 73-10-30 81-09-19 9,110 2,270 1,260 42 102,000
25 109° I08e I07 (
H I NSDALE
A U.S. GEOLOGICAL SURVEY . GAGING STATION AND ' NUMBER--Box around number indicates a NASQAN station MINERAL IRJO Ca SO PREDOMINANT IONS Ca, ^calcium; SO/,, sulfate; Na, GRANDE sodium; HCOo, bicarbonate
367686 ^
40 KILOMETERS
Figure 7.-~Predominant ions at selected gaging stations, October }, 1973 - September 30, 1981.
26 Table 12. Water-quality classification of streaas in the San Juan River basin upstream froa Shiprock, New Mexico
[Ca, calcium; S04 , sulfate; Na, sodium; HC03 , bicarbonate; Cl, chloride; Mg, magnesium]
Classification and frequency of occurrence in percentages Number CaNa Ca Ca Na Na Na Na Na Ca Station of Ca Ca CaNa CaNa S04 HC03 Mg Na Na Ca Ca HC03 S04 Mg Na S04 number Station name samples HC03 S04 HC03 S04 HC03 S04 S04 HC03 S04 HC03 S04 S04 HC03 S04 Cl HC03
09341200 Wolf Creek near Pagosa Springs, Colorado 12 100 ______
09343000 Rio Blanco near Pagosa Springs, Colorado 7 100 ------___
09343300 Rio Blanco below Blanco Div. Dam, near Pagosa Springs, Colorado 7 1 *"\ r\
09343400 Rio Blanco at U.S. Highway 84, near Pagosa Springs, Colorado 5 100 ------____
09344300 Navajo River above Chromo, Colorado 5 100 ______
09346000 Navajo River at Edith, Colorado 9 100 ------____
09347200 Middle Fork Piedra River near Pagosa Springs, Colorado 12 75 _ 25 ------____
09352900 Vallecito Creek near Bayfield, Colorado 39 100 ------_.__
09355500 San Juan River near Archuleta, New Mexico 46 100 ------____
09356565 Cafion Largo Wash near Blanco, New Mexico 9 100 ------
09357000 San Juan River at Bloomfield, New Mexico 3 34 --33 - -- -33------
09357100 San Juan River at Hammond Bridge, near Bloomfield, New Mexico 32 22 37 3 16 - -- - 3------19
09357300 San Juan River above Animas River at Farmington, New Mexico 49 12 43 21 10
09357500 Animas River at Howardsville, Colorado 15 100 Table 12. Water-quality classification of streams in the San Juan River basin upstream from Shiprock, New Mexico - Concluded
Classification and frequency of occurrence in percent.*3£*. Number CaNa Ca Ca Na Na Na Na Na Ca Station of Ca Ca CaNa CaNa S04 HC03 Mg Na Na Ca Ca HC03 so4 Mg NEI SO number Station name samples HC03 S04 HC03 S04 HC03 so4 S04 HC03 S04 HC03 so4 so4 HC03 so4 Cl HC03
09358900 Mineral Creek above Silverton, Colorado 13 - 100
09364500 Animas River at Farmington, New Mexico 47 9 66 17
09365000 San Juan River at Farmington, New Mexico 153 15 51 10 1 12
09367500 La Plata River near Farmington, New Mexico 27 7 26 18 15 26
09367540 San Juan River near Fruitland, New Mexico 33 21 52 15
09367561 Shumway Arroyo near Waterflow, oo New Mexico 61 - - 70 20 10 09367660 Chaco Wash near Star Lake Trading Post, New Mexico 3 - 34 33 33
09367680 Chaco Wash at Chaco Canyon National Monument, New Mexico 17 76 12
09367710 De-Na-Zin Wash near Bisti Trading Post, New Mexico 6 83 - 17
09367930 Hunter Wash at Bisti Trading Post, New Mexico 10 - - 20 80 - -
FC3 Morgan Lake 21 - 33 - 62
FC4 Ash pond Effluent 34 - 100
09367950 Chaco River near Waterflow, New Mexico 33 - 12 27
09368000 San Juan River at Shiprock, New Mexico 164 2 53 27 Metals-mining activities have occurred in the headwaters of the Animas River and probably contribute the sulfate component to the calcium sulfate water passing stations 09358900 and 09357500 (table 12). Further downstream at station 09364500, bicarbonate and sulfate components are present in the water. The La Plata River near Farmington, New Mexico (station 09367500, table 12), contains irrigation-return flow during the growing season, which likely increases the sodium component (sodium is leached from soils). Station 09367561, located on Shuraway Arroyo north of the San Juan River near Waterflow, New Mexico, contains sodium sulfate water (table 12). Effluent from a nearby power plant that flows into the arroyo affects the water-quality classification. Station 09367950 is also affected by effluent from a power- plant operation. Upstream of station 09367950, water is classified as calcium bicarbonate and sodium bicarbonate. At station 09367950, water classification is sodium calcium sulfate.
As the San Juan River exits the study area at the Shiprock station, it is a calcium sulfate water 53 percent of the time and a calcium sodium sulfate water 27 percent of the time (table 12). The water is an integration of the many tributaries feeding the San Juan River. However, the station's water classification does not reflect the variety of water classifications at upstream tributaries or the water classification existing at upstream tributaries for a chosen point in time.
Var i ab i 1 i ty_of Concejntrations or Propejjt^ies of Selecj: e d Water-Quaji t y Constituents
Water-quality data at stations throughout the study area were selected and plotted on maps to show spatial variability. The median value for available data during October 1973 through September 1981 was selected for plotting because it is not biased by extreme values. A median value was plotted at a station only if four or more measurements were made throughout at least 1 year. The data were then considered to be representative for a particular station.
Since the presentation of all water-quality constituents would be too repetitive, eight constituents were chosen. Specific conductance was chosen as a general indicator of dissolved solids. Dissolved sodium was chosen because it is usually a major cation. Dissolved sulfate was chosen because it is usually a major anion. Two metals were chosen: dissolved iron and dissolved manganese. Dissolved-orthophosphate phosphorus was chosen to represent a nutrient constituent. Dissolved radium-226 was chosen to represent radioactive constituents.
29 Medians of specific conductance vary from 50 to 6,570 microsiemens per centimeter at stations throughout the basin (fig. 8). The smallest values are reported from stations in the northeastern mountainous areas where snowmelt contributes largely to streamflow and the drainage areas consist of igneous- rock formations. The largest value of 6,570 microsiemens per centimeter at Shumway Arroyo near Waterflow is due to a point-source effluent from a power- plant facility less than a mile upstream. On the same tributary 4 miles upstream from the power plant at Shumway Arroyo near Fruitland, the median of specific conductance is 850 microsiemens per centimeter. Another large value of 1,800 microsiemens per centimeter at Chaco River near Waterflow is located about 9 miles downstream of a second power-plant facility. Median values of specific conductance ranging from 393 to 981 microsiemens per centimeter upstream from the Chaco River near Waterflow are considered to be due to the dissolution of salts from the sandy and shaly soils. This area of the basin consists of many canyons and ephemeral channels incised in the surrounding sandstone and shale. Some stations in the north-central and northeastern parts of the basin with specific conductances larger than nearby stations probably are impacted by irrigation-return flow that has elevated specific conductances.
The pattern of variation in median concentrations of dissolved sodium in the basin and the reasons for the variation are very similar to those of specific conductance discussed in the preceding paragraph. Median values of dissolved-sodium concentration vary from 1.1 through 1,300 milligrams per liter (fig. 9). The large value of 770 milligrams per liter at the station on Canon Largo is probably due to a small saline-water spring that discharges to the normally ephemeral channel of Canon Largo.
Median concentrations of dissolved sulfate vary throughout the basin in a similar pattern and for the same reasons as specific conductance discussed above. The range in median concentrations of dissolved sulfate is from 4.3 through 3,800 milligrams per liter (fig. 10).
The pattern of dissolved-iron variation in the basin is different from specific conductance, sodium, or sulfate. Dissolved iron varies from less than 10 through 410 micrograms per liter (fig. 11). The largest dissolved- iron concentrations are found in the southeastern section of the basin at stations on the Chaco River and its tributaries. Here, some concentrations are ten times greater than other parts of the basin, or more. In the weathered outcrops of this area, an abundance of iron accumulates as oxide coatings on sand, silt, and clay; as inorganic minerals or organic compounds in the soils; and in plant and animal detritus. Generally, iron is very soluble in acidic water but relatively insoluble in alkaline water. Therefore, the alkalinity of runoff in the area limits the quantity of iron that is dissolved. The larger dissolved-iron concentrations found at some stations may be attributed to ultrafine suspensions of particulate iron compounds, which are difficult to filter from water samples and are analyzed as dissolved iron (Roybal and others, 1983). Dissolved-iron concentrations are largest in areas related to geologic and climatic conditions of large erosion and large sediment concentration in water rather than areas affected by mining, farming, urbanization, and industry.
30 109° 108° 107' 38
GRANDE
MEDIAN SPECIFIC CONDUCTANCE IN MICROSIEMENS PER CENTIMETER AT 25° CELSIUS Gaging stations are shown in figure 6
20 40 MI LES i I 20 40 KILOMETERS
Figure 8.--Variability of median specific conductance, October 1,
1973 - September 30, 1981.
31 109° I 08° 107'
SAGUACHE
MEDIAN DISSOLVED-SODIUM CONCENTRATION, IN MIL LIGRAMS PER LITER MINERAL ! R j O Gaging stations are shown in figure 6. GRANDE
,' PLATA J$/VA£LECtTO( ' . ' \ . . ; 'sw \ RESERVOIR] PAGOSA /! , v SPRINGS f ..- y 7 r
COLORAD< NEW MEXIC 240 SHIP49C
^ #/,^ J ?IVER BASIN BOUNDARY
0 20 40 KILOMETERS Figure 3.--Mar iabi1 Ity of median dissolved-sodiurn concentration,
October 1, 1973 - September 30, 1981.
32 to c
o o rf o> O cr n>CT * w - rt
« O -h l\>_ ^o O 3 Q. 1 O> 0~*> to CO u> 3 Q. rl- X n> 3 r cr O O 2 -5 < m Q H Q. o 1 m « in 3 C w
CO CU I 09° I08C 107* I V_QURAY SAN
. | MEDIAN DISSOLVED-I RON 1 CONCENTRATION, IN MICROGRAMS PER LITER-- MlNERAL IR1 Gaging stations are shown in figure 6 GRANDE
COLORADO NEW MEXIC
20 40 KILOMETERS Figure 11.--Variabi1ity of median dissolved-iron concentration,
October 1, 1973 - September 30, 1981.
34 Median concentrations of dissolved manganese are shown in figure 12 and range from less than 10 to 430 micrograms per liter. Some of the largest values of dissolved manganese, 300 and 340 micrograms per liter, are associated with the metals-mining area in the northern tip of the basin in the headwaters of the Animas River. The largest median concentration of dissolved manganese, 430 micrograms per liter at Shumway Arroyo near Waterflow, is less than a mile downstream from an electric power-generation facility.
Median concentrations of dissolved-orthophosphate phosphorus throughout the basin are shown in figure 13. The range in these medians is from less than .01 to .08 milligram per liter. The largest value of .08 milligram per liter is the median value for the station Shumway Arroyo near Waterflow, which is just downstream from the electric power-generation facility located north of the San Juan River main stem. Other dissolved-orthophosphate phosphorus values appear to be relatively uniform.
Median concentrations of dissolved radium-226 are similar throughout the basin (fig. 14). Medians range from .06 through .10 picocurie per liter. Dissolved radium-226 has the most uniform median concentration of any constituent discussed. Of these water-quality constituents discussed, the NASQAN station at Shiprock, New Mexico, best represents dissolved-radium-226 conditions throughout the basin, due to the uniformity of this constituent.
yariability^ of Loads of Selected Water-Quality Constituents
The product of concentration in milligrams per liter (mg/L) multiplied by streamflow in cubic feet per second (ft /sec) has the units of mass per unit time (mg/L x ft^/sec x 28.23 L/ft^ = mg/sec). This is referred to as a load in this report. Loads are additive and the loads at Shiprock are sums of the loads measured in the upstream tributaries plus any unmeasured contribution. Annual loads were calculated from regression equations between streamflow and constituent load for six of the seven constituents discussed in the previous section: specific conductance, dissolved sodium, dissolved sulfate, dissolved iron, dissolved manganese, and dissolved radium-226. Annual loads for dissolved-orthophosphate phosphorus were not calculated because of the poor relationship between streamflow and load.
The first step in the calculation of an annual load for a constituent was to determine the mathematical relationship between streamflow and load as described by Miller (1951). Instantaneous values of streamflow that had a simultaneous value for constituent concentration were multiplied to obtain a load. The instantaneous streamflow and the instantaneous load were graphed with streamflow being the independent variable and load being the dependent variable. A regression equation was determined for the points on the graph and the r value of the regression equation was noted. A large r2 may result from this regression because streamflow is on both sides of the regression equation (streamflow versus streamflow times concentration).
35 I09C I08g 107*
SAGUACHE
MEDIAN DISSOLVED-MAN- I I GANESE CONCENTRATION, IN MICROGRAMS PER LITER--Gaging stations MlNERAL I RI are shown in figure 6. GRANDE
/VQ'PAGOSA .,-// V; SPRINGS
NEW MEXIC
BASIN BOUNDARY
40 KILOMETERS Figure 12.--Variabi11ty of median dissolved-manganese concentration,
October 1, 1973 - September 30, 1981.
36 109° 108° 107*
EXPL.ANATI ON SAN HINSDALE SAGUACHE M I GUE MEDIAN DISSOLVED-ORTHO- PHOSPHATE PHOSPHORUS CONCENTRATION, IN MIL LIGRAMS PER LITER-- Gaging stations are shown in figure 6. GRANDE
NEW MEXIt?
40 KILOMETERS Figure 13. Variabi1ity of median dissolved-orthophosphate phosphorus concentration October 1, 1973 - September 30, 1981. 37 o o ft 0) o cr cr n> 3 fl> Q. 0) to n> oo n> 3 cr n> 0) Q. CO C 3 o As explained by Younger (1979, p. 234), the r value measures the strength of the mathematical relationship, or when multiplied by 100, the percentage of variation in the dependent variable (load in this case) that can be predicted by the mathematical relationship to the independent variable (streamflow in this case). Regression equations were judged to be adequate predictors of the load only if the r value for the equation was equal to .75 or greater. That is, 75 percent or more of the load could be predicted from a known streamflow volume. If the r value was .75 or greater, the daily mean streamflow was used as the independent variable in the regression equation to calculate a daily mean load. The daily mean load was then summed for all the days of the year to calculate an annual load. If the r value was less than .75, no annual load was calculated. The annual load calculation was further refined if the separation of the streamflow hydrograph into two seasonal periods, yielding two predictive equations, consistently improved the r values. Annual streamflow hydrographs were plotted to determine if there was seasonal variation. At some stations a distinct snowmelt period was very noticeable. At these stations two regression equations were developed to predict daily mean loads for constituents. One regression equation was developed based on streamflow and constituent concentration during the snowmelt period; a second equation was developed based on streamflow and constituent concentration during the rest of the year. Only in the case of station number 09364500, Animas River at Farmington, New Mexico, did the separation of the streamflow hydrograph into two seasonal periods consistently improve the predictive equations. Therefore, a predictive equation for loads during the snowmelt period and loads during the rest of the year was used at this station since it was superior (as judged by the coefficient of determination, r ) to the predictive equation for loads based on the full year's data. For example, for specific conductance the r values were .96 for both the snowmelt and the rest of the year while the r 9 value was .94 for the whole year. At the other stations within the basin, predictive equations for loads were based on data over the whole year, rather than the year divided into a snowmelt and "rest-of-the- year" season. Although specific conductance multiplied by streamflow does not represent a true load and the product does not have units of mass per unit time, the product of specific conductance and streamflow is an indirect measurement of the dissolved-solids load. Dissolved solids can be predicted if specific conductance is known (Hem, 1970, p. 99). The product of specific conductance and streamflow is shown in figure 15 at stations where adequate predictive equations could be developed. The variability of the product of specific conductance and streamflow throughout the basin is an indirect measure of the variability of the dissolved-solids load for the basin. At three stations, specific-conductance data were available from both the WATSTORE Daily-Values File and the WATSTORE Water-Quality File (fig. 15). At two stations, the WATSTORE Daily-Values File data gave a yearly product less than the WATSTORE Water-Quality File data. At the third station the Daily-Values File data gave a yearly product equal to the Water-Quality File data. This would lead to the 39 assumption that samples taken monthly or less frequently may result in higher estimates of the loads. About one-third of the specific-conductance- streamflow product that passes the Shiprock, New Mexico, station (table 13) originates upstream of Archuleta, which is 25 percent of the total basin area; one-third originates in the Animas River basin, which is 10.5 percent of the total basin area; one-eighth originates from the Canon Largo, La Plata and Chaco River basins; and about one-fifth cannot be accounted for and is assumed to originate from small ungaged drainages or to flow to the main stem as overland flow, ground-water inflow, or point sources between the gaging stations at Archuleta and Shiprock. The mean annual product of specific conductance and streamflow per square mile is greatest in the Animas River drainage basin and smallest in the Chaco River and Canon Largo drainage basins (fig. 16). The variability of the mean annual dissolved-sodium load throughout the basin is shown in figure 17. The greatest dissolved-sodium load, 14,500,000 kilograms per year, originates from the large upstream drainage area in the northeastern part of the basin. The next largest loads of 6,040,000 and 5,960,000 kilograms per year originate from the Animas River basin and the Chaco River basin, respectively. A mean annual dissolved-sodium load for the entire basin was not computed at the Shiprock station because of the poor r value for the predictive equation; however, it will be greater than the sum of the measured tributary load inflow. The mean annual dissolved-sodium load per square mile is shown in figure 18. On a per-square-mile basis, the largest loads originate from the northern part of the basin and the smallest loads originate from the southern part of the basin. The variability of the mean annual dissolved-sulfate load (fig. 19) is similar to that of the dissolved-sodium load. No value was calculated for the Shiprock station to determine a total-basin load. The greatest dissolved- sulfate load of 67,800,000 kilograms per year originates from the Animas River basin. The large upstream drainage area in the northeastern part of the basin and the Chaco River contribute the next two greatest dissolved-sulfate loads. On a per-square-mile basis, the greatest loads originate from the Animas River drainage basin (fig. 20). The mean annual dissolved-radium-226 load was calculated at four stations in the basin (fig. 21). The total load for the basin is 113,000 microcuries per year for the NASQAN station at Shiprock. Of that total, about 58 percent originates from the Animas River basin, which comprises only 10.5 percent of the basin's drainage area (table 14). On a per-square-mile basis, the greatest load originates from the Los Pinos River drainage basin (fig. 22). 40 Table 13. Percent contribution to the mean annual product of specific conductance and streamflow by subbasin for the San Juan River basin upstream from Shiprock, Hew Mexico Percent contribution to total product Subbasin and percentage Using WATSTORE Using WATSTORE of total basin area Daily-Values File Water-Quality File San Juan River basin from Archuleta, New Mexico, upstream, 25 percent 32.5 Ca'non Largo basin, 13 percent 2.8 Animas River basin, 10.5 percent 37.2 34.8 La Plata River basin, 4.5 percent 3.3 Shumway Arroyo basin, 0.6 percent 1.0 Chaco River basin, 34 percent 5.8 6.4 Table 14. Percent contribution to the mean annual dissolved-radiua-226 load by subbasin for the San Juan River basin upstream from Shiprock, New Mexico Subbasin and percentage Percent contribution of total basin area to total load Vallecito Creek basin, 0.6 percent 5.1 Animas River basin, 25 percent 57.6 Chaco River basin, 34 percent 2.8 41 I09C 108 I07 e HIMSDALE SAGUACHE RIVER BASIN 351 ,000 ,000 BOUNDARY GRANDE 328 ,000 ,00 W NTEZUMA NAVAJO RESERVOIR |X| 22 ,400,0 RIO ARRIBA SAN JUAN EXPLANATION 18,900,000 _ PRODUCT OF MEAN ANNUAL STREAMFLOW, IN CUBIC FEET PER YEAR, TIMES SPE CIFIC CONDUCTANCE, IN MICROSIEMENS PER CENTIMETER AT 25° CELSIUS-- MCKI NLEY Striped bar indicates data from the Daily-Values WATSTORE File. Solid bar indicates data taken CROWNPOINT .0 from the Water-0.ua! i ty WATSTORE File. Gaging stations are shown in figure 6 40 KILOMETERS Figure 15.--Variabi1ity of the mean annual product of specific conduct ance and streamflow, October 1, 1973 - September 30, 198l 42 94 ,800 109 SAGUACHE SAN Ml GUEL RIVER BASIN BOUNDARY GRANDE PLATA 860SA t DURANOG if/SPR!N6S / 89J70® 7 ( J MO NT E Z UM ARCHULETA R I O AF?R! BA SAN JUAN EXPLANATI ON 5150^ 4340 PRODUCT PER SQUARE MILE OF MEAN ~| ANNUAL STREAMFLOW, IN CUBIC FEET PER YEAR, TIMES SPECIFIC CONDUCT ANCE, IN MICROS I EMENS PER CEf4T|- METER AT 25° CELSI US Striped bar MCKINLEY indicates data taken from the Daily-Values WATSTORE File. Black bar indicates data from the Water- CROWNPOINT .D Quality WATSTORE File. Gaging stations are shown in figure 6 20 40 M I LES _J 20 40 KILOMETERS Figure l6.--Variabi1ity of the mean annual product of specific conductance and streamflow per square mile of drainage area, October 1, 1973 - September 30, 1981. 43 109° 108C 107* I VJDURAY/ EXPUANATI ON SAN \ ^.H SAGUACHE I 90,700 1 " MEAN ANNUAL DIS- I SOLVED-SODIUM LOAD, IN KlLOGRAMS--Gaging stations are shown in figure 6, GRANDE / SPRINGSf J r MONTEZUMA. ARCHULETA COLORADO NEW MEXIC 5 ,960 ,000 MORGAN X LAKE RiO ARRIBA N &IVER BASIN BOUNDARY 0 20 40 KILOMETERS Figure 17.--Variabi1ity of the mean annual dissolved-sodium load, October 1, 1973 - September 30, 1981. 109° 108C 107' EXPLANATION SAGUACHE MEAN ANNUAL DIS- SOLVED-SODIUM LOAD, IN KILOGRAMS PER SQUARE MILE--Gaging stations are shown i n figure 6. GRANDE \LEMON SEft- VOIR RiNGS < J MONTEZUMA. ARCHULETA COLORADO NEW MEX1C R1O ARRIBA N SAN JUAN ?IVER BASIN BOUNDARY MCKINLEY 0 20 40 KILOMETERS Figure l8.--Variabi1ity of the mean annual dissolved-sodium load per square mile of drainage area, October 1, 1973 - September 30, 1981. 45 109° 108C 107* V»OURAY/ HI SAGUACHE I MEAN ANNUAL DISSOLVED- SULFATE LOAD, IN KILO- GRAMS Gaging stations are shown in figure 6 GRANDE 9,930/0 COLORADO NEW MEXIC 0 20 40 KILOMETERS Figure 19."Variabi 1 i ty of the mean annual di ssol ved-sul fate load, October 1, 1973 - September 30, 1981. 46 73 ,700 109' 38 EXPLANATION SAN ) HINSDALE SAGUACHE MI GUE MEAN ANNUAL DISSOLVED- SULFATE LOAD, IN KILO GRAMS PER SQUARE MILE-- Gaging stations are MlNERAL I R i o shown in figure 6 GRANDE /'VAtlLECITO RESERVOIR. ; ( J MONTEZUMA. ARCHULETA COLORADO NEW MEX1C RSO ARRIBA N f(IVER BASIN BOUNDARY SANDOVAL 40 KILOMETERS Figure 20.--Variabi1ity of the mean annual dissolved-sulfate load per square mile of drainage area, October 1, 1973 - September 30, 198l. 47 I09C I08C I07 C V.QURAY/ \ J^HINSDALE SAGUACHE | MEAN ANNUAL DISSOLVED- RADIUM-226 LOAD, IN MICROCURIES--Gaging Ml NERAL I RI o stations are shown in figure 6 GRANDE \RESEKVOIR. Ui COLC =!ADO NEW ^ EXiC IJUVER BASIN BOUNDARY 40 KILOMETERS Figure 21.--Variabi1ity of the mean annual dissolved-radium-226 load, October 1, 1973 - September 30, 1981. 48 I09C 108C 107* I V.QURAY/ SAN X.XHINSDALE MI GUEL/"l / * MEAN ANNUAL DISSOLVED- RADIUM-226 LOAD, IN MICROCURIES PER SQUARE MILE--Gaging stations are shown in figure 6. GRANDE PAGOSA / INGS / ( J COLORADO NEW MEX1C ?IVER BASIN I BOUNDARY 40 KILOMETERS Figure 22.--Variabi1ity of the mean annual dissolved-radium-226 load per square mile of drainage area, October 1, 1973 - September 30, 1981. 49 Box-and-Whisker Plots Box-and-whisker plots (Gerig, 1980) show the distribution of water- quality and streamflow data for a chosen period in time. The box-and-whisker plot identifies the mean, median, the 25th and 75th percentiles of the data, adjacent values, and extreme values of the data set. The adjacent and extreme values are calculated as described by Tukey (1977, p. 39-48). Extreme values are subdivided into the terms "outside" values and "far-out" values. Values greater than 1.5 times the interquartile range (difference between the 75th and 25th percentiles) are outside values, and values greater than 3 times the interquartile range are far-out values. Dissolved-orthophosphate phosphorus, dissolved-iron and dissolved- manganese data contained values reported as less than a given laboratory detection limit, which was subject to change during 1974 to 1981. If a value was given as less than 10 micrograms per liter, for example, it is known to be between 0 and 10 micrograms per liter. In order to simplify matters and avoid bias by either deleting the data or choosing the upper or lower limit as a substitute for the less than value, the midpoint of the known range was chosen, 5 micrograms per liter. That midpoint value replaced the original less than value in the data set. This new data set was then used to produce box-and-whisker plots. For comparison purposes, the box-and-whisker plots are shown side by side and at the same scale for 23 stations in the study area except figure 23, which shows a box-and-whisker plot for 16 stations (figs. 23-32). It can be seen that streamflow has a large percentage of far-out values (fig. 23). The streamflow box-and-whisker plots have the longest tails of far-out values. This implies that streamflow at most stations is highly variable, also highly skewed and nonnormal. Streamflow from station to station also is quite variable. Streamflow affects water-quality constituents through dilution processes. Dissolved-iron (fig. 24) and suspended-sediment concentrations (fig. 25) are the water-quality constituents with the most noticeable percentage of far- out values. The central values (25th percentile, mean, median, and 75th percentile) for dissolved iron are poorly defined on the plot due to the scale. Central values for suspended sediment are fairly variable. Dissolved radium-226 (fig. 26) is the constituent with the least number of far-out and outside values. It also does not vary greatly from station to station. Specific conductance (fig. 27), pH (fig. 28), dissolved-orthophosphate phosphorus (fig. 29), dissolved sodium (fig. 30), dissolved sulfate (fig. 31), and dissolved manganese (fig. 32) fall between dissolved iron and dissolved radium-226 in variability at a single station. Central values of specific conductance and sulfate are the most variable from station to station of this group of constituents. 50 Station 09367561, Shumway Arroyo near Waterflow, New Mexico, has the greatest variability of all stations for most constituents and the largest concentration for these constituents. It has the greatest variation in specific conductance, pH, dissolved-orthophosphate phosphorus, dissolved sodium, and dissolved sulfate. This station carries wastewater from a power- generation facility located less than a mile upstream, except in the case of a rainfall event, when it carries a mixture of wastewater and overland runoff. The conclusion could be made that effluent from power-generation facilities adds the largest concentrations of the above-named constituents to the stream system. The box-and-whisker plots show that large concentrations of the following constituents are transported to the San Juan River main stem from the Canon Largo tributary, station 09356565: dissolved sodium, dissolved sulfate, dissolved manganese, and suspended sediment. Compared to streamflow in the main stem, flow in this tributary is small, emanating from small seeps and springs except when there is a rainfall event. Then, a mixture of ground- water flow and overland runoff is carried and the streamflow volume is large. The box-and-whisker plots of sulfate, specific conductance, and pH at stations FC6 and 09368000 represent data collected at the same site by two different organizations. Only in the case of dissolved sulfate do the box- and-whisker plots appear to be very similar. Box-and-whisker plots of specific conductance at these two stations are fairly similar. Box-and-whisker plots of pH are noticeably more compressed for station FC6 than for station 09368000. The compression in pH at FC6 could be due to the fact that data from this station are monthly averages rather than instantaneous values and this could have a leveling effect. At station 09368000, pH measurements were taken at the time of collection. The box-and-whisker plots display variations in the data better than the summary values of tables 1 through 10. The tables give maximum and minimum values that indicate degrees of variation but do not show the values that are near these extremes or the spread about the central values. The two NASQAN stations, Animas River at Farmington (09364500) and San Juan River at Shiprock (09368000), have large volumes of streamflow. Of the stations shown in figures 23 through 32, the two NASQAN stations are low in variability; that is, their box-and-whisker plots are compressed. Their constituent concentrations are also at smaller levels in comparison to other stations in the basin. In general, stations with small to ephemeral flows in the downstream end of the basin have the most variable water quality and often have large constituent concentrations. These stations have little influence on water quality in the San Juan River main stem, but they are representative of conditions in the southern part of the basin. 51 STREAMFLOW, IN CUBIC FEET PER SECOND K» *« -"*." -n 0 2 5 S 2 o o o o o o o o LQ C -\ | 1 1 1 1 (D N3 ^X> » i 1 + i 3 » 1 09352900 0«»»» >» + + 1 r^ 3E 3 ~-i 3» 0 -1 00 t^i --n m t^i O 3* -H O J> t C- i 33 O X Z X 3> <-" ' X -f»« 4 3»f~> O 1 0935S500 QJ 33 33 -H 13 o (-> «: < m m < 3» 3> Q- Z Z 3» r- r- 1 t I i c= c= 09356S65 c s r r m rr i/i 7T fl> 09357100 -\ -o (A H 09364500 - ,*~i_ c », ,.,,»»...».».».»»»..»» » O > rt H O-h 0 Z 09366500 o' » * « » to rt -\ 0 0> m 09367500 <=>» » Q) z 3 -h H O T| 09367540 O 0. Q) > rt -{ 09367561 o » Q) " 0 O z 09367680 ;J * * 0 rt z O c cr 2 (t . -\ 0) 09367685 » > m a 09367710 U) -^i ^A) » 4 1 09367930 , CO (t) -a 09367938 » . . rt (t) 3 cr n> -\ > ^A) O s. 00 21.000 * fAR-our vAi.ur f) OIIISIUF VALIIt | AO.IALENT VALIJT 17.500 t-4 7bTH CERCENTILE + HFAN *-* MEDIAN 4 -t 25TH PtRCfNI ILE 10,600 Ln U) STATION IDENTIFICATION NUMBER Figure 2k. --Box-and-whisker plot of dissolved-iron data, October 1, 1973 - September 30, 1981 534.000 TAR-OUT VAIIIF OtIISIUL VALUE ADJACENT VALUF 445.000 75111 PERCFN1 HE MEAN z *-* MEDIAN o 1-+ 25TH PERCENI 1LE MB C H < a ^ }ll 356.000 Z - hi J () U z a ) O U u DL H W * * J | 267.000 * s a * - o * Q - A U J in -i * i - * Ui OS * * -P- hi * Q Z 178.000 * * * Z " 0 * * hi 4- 4 0 * DL t * ft * 3 0 in 0 0 0 * 0 0 0 0 < 1 0 1 60,000 | +-4 0 | 0 1 II 0 +-+ | 4-t III 1 Ml *-* | *+* 4 ++« *-. | | * « 4-4 | | | | | | *+ Ml +-* *-* *- +-* 1 1 * * *-* 1 *- + + -* 1 II o o * +04 +-4 | III! 0 STATION IDENTIFICATION NUMBER Figure 25.--Box-and-whisker plot of suspended-sediment-concentration data, October 1, 1973- September 30, 1981. * FAR-OUT VALUF 0 OUTSIDE VALUE | ADJACENT VALUE + -+ 75TII PERCENT1LE + MEAN K *-* MEDIAN LU D. ^ -i 25TH PERCENT)LE W lil 0.4 I 0.3 0.2 I I I 4-4 I I I I I I l + l I I I I I *-* 4-4 *-« I I I 4- + 4-4 I «4* 4-4 STATION IDENTIFICATION NUMBER Figure 26.--Box-and-whisker plot of dissolved-radium-226 data, October 1, 1973- September 30, 1981 SPECIFIC CONDUCTANCE, IN MICROS I EMENS PER CENTIMETER AT 25° CELSIUS 4 *V -> «D 9 b c', 10o Wo o0" oO oO Cc -n 1 1 1 1 1 1 4 ID FC1 + » c -5 4 * * n> !'!+ * * 4. » 4. FC2 * ' 1 4. ' 0 » 4- » 4. NJ 004-0 cnmmviCJC^ ^ FC3 » 1 O J» HO H 3O 1 I Z X > VI I J» O »- O 1 CO » o 1 + 1 » » m m z m H FC4 + » * 30 30 -1 0 O O «= «= c/o X + »+ zzs»r- i n> 1 I i * o o»»» » i i r~ c c cu FC5 * » + »-«c:mm rt i i m * n> CL + o 3 i FC6 cr 5[ n> IT -i Ul 09352900 c > v» 7T to o CD ^ -^ > ^ ^ 09355500 CO 0 0 rt z 09356565 O * 4- -h 09357100 4- 0 » D » * in n Z 4- 0) 4 09364500 0 1 0 O M T! + -h 09365000 1 0 » * » n 0 i > 09366500 1 4- 1 o H 0 0 T~ TT * CL 09367500 +_ » C Z 0 rt z 09367540 1 4- O QJ c O 2 n> a 09367561 m CL n QJ rt 09367680 » 0 » QJ 09367685 1 4- 0 » » * * O O rt 09367710 O 4- 0 0 » O » + CT n> 4- » 4- -5 09367930 1 1 4- 00* » 4. » 4- -"* 09367938 » 1 1 O » » » Co 4- » 4- 09367950 O^ 1 4- 1 . o » » » » * c^ 4- » 4- 1 09368000 4- 1 0 » » * » 4> 1 1 1 1 1 11.0 9.5 ( I I I I I I I i i i I I I I I I I I I I I +-+ I I I * * * I I I I I I + -4 0 I I +- » I 0 0 I I I I I o X a 6.5 5.0 - FAR-OUT VALUE 0 OUTSIDE VALUE 3.5 | ADJACENT VALUE -+ 75TH PERCENTILE *-* MEDIAN -+ 25TH PERCENTILE 2.0 STATION IDENTIFICATION NUMBER Figure 28.--Box-and-whisker plot of pH data, October 1, 1973 - September 30, 198l DISSOLVED-ORTHOPHOSPHATE PHOSPHORUS IN MILLIGRAMS PER LITER to ! 1 1 1 I c -1 FC1 (D * * * N> FC2 ' 1 + ' 0 * UD fxa 3 3 -^J > O ' 1 FC3 3 ^» . O 33 CD ~~ > O ^ O FC4 o X i i 2 x = o 1 n m = > > It Qj z Z > r- o FC5 Z Z - ^ ^ cr CL r -n (D i n §- FC6 ~* in7\~ 09352900 * ' (D v£> "^ 2470 1230 617 STATION IDENTIFICATION NUMBER Figure 30.--Box-and-whisker plot of dissolved-sodium data, October 1, 1973 - September 30, 1981 B3UU V1 * FAR-nill VALUF n (HITS I OF VAI UE AD.lACt Nl VAI ll[ U 6920 4-t 751 M PfRCFNllLE H + Ml AN -" *-* MEDIAN K f- + ?5TH PERCtNTILE hi Q. 2 5530 - K " 41 O * -1 * S 4150 4 - * *h Ul H * U. * -1 3 2770 * * 0) 0 1 o 4 0 + -4 Q 1 Ul * -1 O 1*1 1 4-4- V) 1 1 _ 1380 4-t | 4-4 1 1 1 Q 1 1*1 1 1 1 o *-* 1*1 4-4 * 1 1 *- * *4* * 0 || 1 1 1 0 1 1 - *4 * 4-4 * *-* 4-4- y 4 - 4 * 4-4 * * * |4 | * 1 1 o 0 *-* 0 4-4 * 1 o *-+ * 4-4 444 0 | *-+ *4«4-+ *4» * *4* * 4* * 4 * | * 4 * 404 *4* *Q* *- *4» »4* i n i i * 4 * 1 1 1 0 1 1 " 1 « 1 1 " * " II 1 STATION IDENTIFICATION NUMBER Figure 31.--Box-and-whisker plot of dissolved-sulfate data, October 1, 1973 - September 30, 19&1 8800 * TAR-OUT VAI HE 0 OUTSIDE VAIHE | AD.IACfNl VAUIF 7330 (- i /Sril t'LRCI NI I I E + MEAN *-* MEDIAN +-+ ?5TH PERCENTILE 2 5870 O DC (J 5 Z 4400 O 10 I I STATION IDENTIFICATION NUMBER Figure 32.--Box-and-whisker plot of dissolved-manganese data, October 1, 1973 - September 30, 1981 TEMPORAL VARIABILITY OF WATER QUALITY Is the water quality in the San Juan River basin getting better or worse? The answer depends on how one chooses to define "better" and "worse." An objective of this study is to define whether the water quality is changing over time and, if so, how it is changing over time. The time period of interest for this study is October 1, 1973, through September 30, 1981. The primary stations of interest are the NASQAN stations, San Juan River at Shiprock, New Mexico, and Animas River at Farmington, New Mexico. Also of interest is whether other stations within the basin correlate with the NASQAN stations. Two analytical techniques were applied to the data. The first is a statistical technique that analyzes for a monotonic trend in monthly or seasonal data. This technique is referred to as the "Seasonal Kendall test for trend magnitude" (Crawford and others, 1983). The second is a graphical technique that displays data values over time and is referred to as time- series plotting. Seasonal Kendall Tejt for Trend Magnitude The Seasonal Kendall test for trend magnitude was performed for data at 36 stations within the study area. Constituents tested include specific conductance, pH, dissolved-orthophosphate phosphorus, dissolved sodium, dissolved sulfate, dissolved iron, dissolved manganese, dissolved radiutn-226, and suspended sediment. Not all of the constituents were tested at each station. Only those constituents that were collected regularly for 3 or more years were selected for testing. At eight stations, the only constituent with sufficient data for testing was specific conductance. A trend was judged to exist if the test was significant at the 5-percent probability level. The hypothesis tested was that there was no trend from October 1, 1973, through September 30, 1981. The hypothesis was declared true (that is, a trend does not exist) if the calculated probability exceeded a given value called the significance level. The significance level chosen for this study was 0.05 (5 percent). The hypothesis was declared false (a trend exists) if the calculated probability was less than 0.05. Using the 5-percent level of significance, a station will appear to have trend when it truly does not have trend once in 20 trials by chance alone. Therefore, in using the 5- percent level of significance, an error will occur once in 20 trials on the average. Trends were detected at 14 stations. Trends detected at the 14 stations and a trend summary for the NASQAN stations are given in table 15. 62 Of the 14 stations where trends were detected, 5 stations are downstream from coal-mining and power-generation facilities. Water-quality measurements taken at these stations may be reflecting changes in coal- or power-production rates over the indicated years and changes in water-discharge practices. The five stations are 09367561, 09367950, FC3, FC4, and FC5 in table 15 and figure 6. Station 09367561 is less than a mile downstream from one coal-mining and power-generation facility; stations 09367950, FC1, FC3, FC4, and FC5 are 9 to 10 miles downstream from a second coal-mining and power-generation facility. The largest increasing trends in specific conductance, dissolved sodium, dissolved sulfate, and dissolved iron and the largest decreasing trend in pH took place at station 09367561. This trend is believed to be associated with wastewaters from the power-generation facility. During 1974 through 1981 this facility gradually increased coal and power production and installed air scrubbers that require the use of water that consequently may have changed the water-quality characteristics of wastewater discharges from the facility. The quantity of flow at this station is small and the trends detected here were not detected at the NASQAN station, 09368000, 18 miles downstream. At the four other stations affected by wastewater flow from the second power- generation facility, the largest decreases in specific conductance, dissolved sodium and dissolved sulfate were detected. A small decrease in pH also was detected for this station. At this facility production remained steady during 1974 through 1981, but efforts to reduce wastewater discharges may account for the decreasing trends. At other stations in the study area, one showed an increase in suspended sediment; one a decrease in suspended sediment; one an increase in dissolved iron; one a decrease in dissolved iron; three a decrease in pH; one an increase in dissolved-orthophosphate phosphorus; one an increase in dissolved sulfate; and one a small decrease in specific conductance and dissolved sodium. These trends may be due to new or increased disturbances in the drainage area, such as expanded metals mining, changes in agricultural practices, or increased urbanization. None of the trends detected above are attributable to any single cause. At the two NASQAN stations, Animas River at Farmington and San Juan River at Shiprock, which appear in boldface type in table 15, a decrease in suspended sediment of 78 mg/L per year occurred at the Farmington station and no trends occurred at the Shiprock station. The decrease in suspended sediment is assumed to result from the retention of sediments in upstream reservoirs and efforts to decrease erosion from farmed lands through improved farm management. Also of some influence may be the land-use change from farms to resort properties in this part of the basin. The NASQAN station 09368000, San Juan River at Shiprock, which is the most downstream station in the study area, is an integration of trends over the upstream basin. No trends were detected at 09368000. At upstream sites there were both increasing and decreasing trends for several constituents and they likely cancelled each other. The Four Corners data-collection site at the same location, FC6, showed a decreasing trend in pH of .04 unit. The most consistent trend in the basin was the decrease in pH at six stations. Three stations are downstream from coal-mine and power-generation activities. 63 Table 15. Results of Seasonal Kendall test for trend magnitude [NASQAN stations in boldface type; mg/L, milligrams per liter; /*g/L, micrograms per liter; S/cm, microsiemens per centimeter at 25 °Celsius Water years Station name that trend and number Trend was detected Vallecito Creek near Decrease in pH of 0.08 unit 1974-81 Bayfield, Colorado, per year 09352900 Increase in suspended sediment of 0.2 mg/L per year Canon Largo Wash Increase in dissolved iron of 1978-81 near Blanco, New 20 /ig/L per year Mexico, 09356565 San Juan River at Decrease in suspended sediment 1978-81 Hammond Bridge, of 218 mg/L per year near Bloomfield, New Mexico, 09357100 San Juan River above Decrease in dissolved iron of 1974-79 Animas River at 2 /<.g/L per year Farmington, New Mexico, 09357300 Animas River at Decrease in suspended sediment 1974-81 Farmington, New of 78 mg/L per year Mexico, 09364500 San Juan River at Increase in dissolved-orthophosphate 1974-81 Farmington, New phosphorus of .01 mg/L per year Mexico, 09365000 La Plata River at Increase in dissolved sulfate 1978-81 Colorado-New of 55 mg/L per year Mexico State line, 09366500 Shumway Arroyo Increase in specific conductance 1974-81 near Waterflow, of 367 ^S/cm per year New Mexico, 09367561 Decrease in pH of .38 unit per year Increase in dissolved sodium of 160 mg/L per year Increase in dissolved sulfate of 200 mg/L per year Increase in dissolved iron of 20 per year 64 Table 15. Results of Seasonal Kendall test for trend magnitude - Concluded Water years Station name that trend and number Trend was detected Chaco River near Decrease in specific conductance 1976-81 Waterflow, New of 230 ^.S/cm per year Mexico, 09367950 Decrease in dissolved sodium of 16 mg/L per year Decrease in dissolved sulfate of 120 mg/L per year San Juan River at No trends 1974-81 Shiprock, New Mexico, 09368000 San Juan River near Decrease in specific conductance 1974-81 Hogback, FC1 of 11 fj.S/cm per year Decrease in pH of 0.06 unit per year Decrease in dissolved sodium of 11 mg/L per year Morgan Lake, FC3 Decrease in specific conductance 1974-81 of 95 ^LtS/cm per year Decrease in sodium of 30 mg/L per year Decrease in sulfate of 45 mg/L per year Ash pond Effluent, FC4 Decrease in specific conductance 1974-81 of 120 fj.S/cm per year Decrease in pH of .12 unit per year Decrease in sulfate of 66 mg/L per year Chaco River down Decrease in specific conductance 1974-81 stream of FC5 of 300 yuS/cm per year Decrease in pH of .02 unit per year Decrease in dissolved sulfate of 190 mg/L per year San Juan River at Decrease in pH of .04 unit 1974-81 Shiprock, New per year Mexico, FC6 65 T^itne_-Series Plots Time-series plots show changes over a period of time for some constituents of interest. Time-series plots were prepared for 1974 through 1981 water-year water-quality data at 36 stations within the study area. Constituents graphed include specific conductance, pH, dissolved- orthophosphate phosphorus, dissolved sodium, dissolved sulfate, dissolved iron, dissolved manganese, dissolved radium-226, and suspended sediment. Any trends detected by the Seasonal Kendall test for trend magnitude may be able to be verified by the time-series plots. From the large number of plots, only selected plots representing some typical conditions and some trends (figs. 33- 43) are presented in this report. Some of the plots showed seasonal variation (figs. 33, 35, and 37). These plots are for stations located north of the San Juan River main stem, located on perennial, high-altitude streams. Concentrations of dissolved chemical constituents are smallest during snowmelt runoff in the spring and largest during late summer when streamflow is small. The following conclusions were made after visual examination of the time- series plots. The determination of whether trends exist may be difficult for many of the plots because of seasonal variation at some stations and sparsity of data. At other stations with plots of extremely large and small values, such as suspended-sediment concentration, the pattern of the smaller values is hidden and trends are difficult to detect. Only at stations 09367950 (fig. 39), FC1 (fig. 42), and FC3 (fig. 43) are sequences with successive, consistent increasing or decreasing members (monotonic trend) readily discernible in the plots. At station 09357100 (fig« 34) a step decrease in specific conductance took place between October 1, 1978, and October 1, 1979. The time-series plots at the two NASQAN stations, 09364500 and 09368000 (figs. 35, 36, 40, and 41), for specific conductance, dissolved sodium, and dissolved sulfate show correspondence, particularly for the periods of small concentrations. The other constituents do not correspond very well. Station 09364500 has more distinct seasonal variation. Most of the constituent values are within the same order of magnitude for the two stations, with the exception of dissolved-orthophosphate phosphorus and suspended-sediment concentrations. Specific conductance, dissolved sodium, and dissolved sulfate appear to be the most stable constituents. The other constituents are more transitory in nature and consequently more changeable at each site through time. 66 1 1 1 8.5 - - 8.0 - 7.5 - 7 .0 - - 6.5 I !...... _.. 40 1 i i 30 20 - 10 _ 0 ,, . Mi.ilm II II h i , Jilhli i, In if , i i i Illh 1974 75 76 77 78 79 80 1 98] WATER YEAR Figure 33."Time-series plots of pH and suspended-sediment concentration, October 1, 1973 - September 30, 198l, at Vallecito Creek near Bayfield, Colorado (station 09352900). i 1 1 oc cc. £ 3 40 ,000 - . tj UJ 0. Z wo £< 20 ,000 - - a o ul 0 i z 0 1 h... 1.. .,., I , a.Ul Ul tooo CO Ul OC o ui 800 - z a. . i- CO 0 H " l! 400 - . o : a. 200 Illl ilii Hi 1974 75 76 77 78 7 9 80 1981 WATER YEAR Figure 3^. "Time-series plots of suspended-sediment concentration and specific conductance, October 1, 1973 - September 30, 1981, at San Juan River at Hammond Bridge near Bloomfield, New Mexico (station 09357100). 67 DISSOLVED-ORTHOPHOSPHATE SPECIFIC CONDUCTANCE, DISSOLVED SODIUM, PHOSPHORUS, IN MILLI IN MICROS IEMENS PER IN MILLIGRAMS PER LITER GRAMS PER LITER CENTIMETER AT 25° CELSIUS o o o J 00 00 00 U» O N *" O> C O 0 C 3 cn o o (3 0 0 0 < 3 to o> ti c5 O O 1 5 9 z. 0 -o 3 to CD O ZT CD si S rt Cu 1 tk O rt (S> 2 cr CD CD - CD CD -i ZT CD O ' O W si O - ui Ul "O ~O x""-*. ' T" - UD O O rt *-^l -i rt CU WJ C in 1 O o n -h si zi co o O) CD Zl W O T3 O "O ^D rt CD CD ^o CD n o O"^ 3 ft1 -t- CT -i -h oo Ui CD Cu si O -! rt O si =_u 5E O ^o O O O Zl O-3 a. CU C V£> Zl O OO d. rt 00 ' CU o Cu en CD o > ~o Zl < ZC CD » to 3 a. __ __ cu i a. (Si (Si ' O tn 73 Q. (S> 0 < C. CD 3 < 00 -! CD o o a. Cu O 1 rt Z3 O O -! ~n CD rt CU Zl ZT -1 rt O ~ 3-iTJ to cu zr ZI rt 0 CQ (SI 1 1 O ZI SUSPENDED-SEDIMENT CONCENTRATION, DISSOLVED MANGANESE, IN DISSOLVED IRON, IN DISSOLVED SULFATE, IN IN MILLIGRAMS PER LITER MICROGRAMS PER LITER MICROGRAMS PER LITER MILLIGRAMS PER LITER UD C -5 CD 1 1 H _ _N CO 3 3 cn CD^ CU CD rt 3 I CU rt UD cn rt CD CU CD 3 3 -5 O cr CD . 13 CD cn CD -5 CD cn O » U) V^nJ ^j V^J O CU __, (T* - 3 O -C- CL rt VJ1 » cn O U) Lfl O OO C O x ' ' cn -h CD Q. CU 3 . rt Q. cn CD cn J> Q. O 3 1 _i . cn < 3 CD CD CU CL Q. cn 1 3 cn po CD c " 13 -h CD CU -1 n rt o CD CD rt n -r\ CD Q. CU rt cn -5 \ cn 3 CU O rt UD O CD rt 3 Q. O cn i " -i O 0 z n 3 CD rt » S 0 CT Q. 2 CD _. CD -1 cn X cn _-» O n « _i o < * CD VjD Q. *«vl I DISSOLVED SULFATE, IN MILLIGRAMS PER LITER IQ fe 09 C o o -\ o o o (T> KJ<0 fe 3 UJ (D v»o l/i (T> KJ I T Ul CO CO (T> ' pt 3 O 0) cr pt KJ pt QJ v. (D pt Q. Q) I O rt l/i 3 C O QJ 00 UJ v-o - Ul o o KJ tt> __. n T o> 0) pt Pt o O D 00 O - o O o T o 0) Pt Q. o A O cr «0 (D 00 M> 1 1 SPECIFIC CONDUCTANCE, DISSOLVED IRON, IN IN MICROS IEMENS PER MICROGRAMS PER LITER DISSOLVED SULFATE, DISSOLVED SODIUM, pH CENTIMETER AT 25° CELSIUS IN MILLIGRAMS PER LITER IN MILLIGRAMS PER LITER UD C ro t o c (D OO 1 1 2 _, Q. 3 (D VD (D Z. -»J (7) 1 2. VjO I/) I/) 0 (D (D 1 i -1 X < « « CO (D (D O (D Q. (7) 0 -o 1 r-t (SI -Q ^-^ (D C i (/> 3 1 0 r-t cr -h r-t Ol (D 0) I/) r-t n rt (D O O V^J >+ -h 3 0 <« 0> (7) O D -o \£) > Q. (D v^o U3 O cr* oo Q. -h vn * U) vj CT* U) O i 1 ' Q) 0 > - r-t . O < 0 CO (D 33 IT Q. Q. C 1 C 3 O 0) O o> < 3 33 O > O (D -^ 0 « -5 3 O o o < (D IE » 0 r-t 33 O> (D 0> 33 0) r-t Q. -1 0 Q_ ^ D 0) (7) (D O ~1 O 1 -h o < j r-t (D 0 0 D. £ D" I -* (D (/) -J O Q. i* C 3 SPECIFIC CONDUCTANCE, DISSOLVED SULFATE, DISSOLVED SODIUM, IN MICROSIEMENS PER IN MILLIGRAMS PER LITER IN MILLIGRAMS PER LITER CENTIMETER AT 25° CELSIUS 0 0 o o o 1 1 to cr gureplotsspecific39.ime-seriesof--Tconductanceandd -in> SJ w 0 CO KJ at Cu concentrations,1,Septem-1973ssolanddived-sulfateOctober- r-t- O IT cu o 0 KJ SJ n> SJ cu 00 cu rt CD -h SJ to O 0) t/> t/> 00 0 o 2 n> X (D Q. - o 1 o U) O Q. to c/> 00 C Cu r-t- 3 1 1 O DISSOLVED-ORTHOPHOSPHATE SPECIFIC CONDUCTANCE, DISSOLVED SODIUM, PHOSPHORUS, IN MILLI IN MICROS IEMENS PER IN MILLIGRAMS PER LITER GRAMS PER LITER pH CENTIMETER AT 25° CELSIUS LQ 00 C o -f O o o rt 3~ O CT o (D (D _» Ql _ , ^ VX> rt 0 "-J n> rt 2 in -rj (D 3- X 1 O o -h O CO i/> o (D 3- W ^-^ rt o (D c/> (D -^ 0 rt 3 C Ql cr l/> -h rt (D 0 0 Ql 3 3 O Q. O O O « 3 V.D Q. Q_ V/o ' O~^ C ^D (/) 0 CJO CO C/> rt O 1 O Ql O « __i 3 O < 0 * ' Ql (D (D rt Q_ v 1 CO l/> -rj QJ O n: 3 Q. vt C_ C Ql C 3 3 QJ Q. 3 0 0 Q. >D 3 0 l/> < n> l/l (D 3 O r-f QJ QJ (D rt r* Q. 1 SUSPENDED-SEDIMENT CONCENTRATION, IN DISSOLVED SULFATE, MILLIGRAMS PER LITER DISSOLVED MANGANESE, IN DISSOLVED IRON, IN MICROGRAMS PER LITER MICROGRAMS PER LITER IN MILLIGRAMS PER LITER C (D .e- 1 1 1 2 _ j 3 3 (D vu CD (D X »>J 3J I VAJ UD V O CD (D o 1 3J -t CD s CO I/) (D 1/1 CD (D l/i i-t- TJ >» ~o CD i-t- r-h CD CD i . 3 ^J O O cr Q. i-t- 3 CD V -^ (fi o C O v-o (ft -h ^D ^ V«AJ O ON V. (D Q. OO 3 O __» O. I/) O V^J (D (ft O oo CX O > .- __» 1 < V I/) < (D CD CD Q. Q- i-t- . 1 3 l/i CO CD C CD D rt- -h CD c_ O r-h c o CD CD D >» 3J O (D CX JO 13 . rt 1/1 ^ < (ft CD CD r-t- o n ' CD O (D r-t- 3 CX V) 1 CO " ET. O O ~o o D n r-t- >» o O o CT Q. 7T CD ~' ~* l/> Z _» O (D V. S < CD CX I SPECIFIC CONDUCTANCE, IN MICROS IEMENS PER DISSOLVED SODIUM, pH CENTIMETER AT 25° CELSIUS IN MILLIGRAMS PER LITER to c ^ M 00 00 w o> to 00 o o (30 0 i (D tk 00 N O) c> o o -c- 1 1 1 1 1 1 1 K> 1 to 1 M -H *» co cn 3 QJ O (D D CL 1 cn luanRiveri UI concentrajm plots;ries< _> rr U rt -h - - QJ O 7T 13 cn CD * "D (D rt O O SJ O 0 rt -h 20 O CT O -s (D QJ O SJ CL 09 i c QJ O ^" U3 rt fl> *-J QJ 0 Z 1 (D si i « - «£> (D T5 X (D 3 QJ O 0- 13 O (D CL 00 O - v CL rt o cn QJ cn rt O O VD < 3 CO (D «£> CL 00 -n -. i m* 0 -* QJ 1 1 1 1 1 1 1 SPECIFIC CONDUCTANCE, DISSOLVED SULFATE, DISSOLVED SODIUM, IN MICROS IEMENS PER IN MILLIGRAMS PER LITER IN MILLIGRAMS PER LITER CENTIMETER AT 25° CELSIUS UD C -1 N Ik 0> 00 c CD O O O O c -^ 1 oi oi o i o c . V^O i i , i i 1 1 to Ik cr QJ 3 CD 3 CD -5 Q. (fi VjO Q. CD o -5 SI CD U> U3 CO QJ SI r-t- 0> ssolived-sulconcentrations,fateSeptem1,October1973- 2 0 -5 specificjlotsofconductanceanddissol - in QJ 13 si 1 SI QJ 7T CD _ . V Z CD si Z. 00 2 CD X O o SI to (f> rt Qj r-t- O =1 00 ~r\ O o CD VjO Q. 1 U> 0 Q. to C 00 i i i ADEQUACY OF NASQAN DATA TO REPRESENT WATER QUALITY THROUGHOUT THE BASIN Water quality is variable throughout the San Juan River basin from Shiprock, New Mexico, upstream. Water-quality types found within the basin include: calcium sulfate, sodium sulfate, calcium bicarbonate, and sodium bicarbonate (fig. 7). The median values of specific conductance and median concentrations of dissolved sodium, dissolved sulfate, dissolved iron, dissolved manganese, and dissolved-orthophosphate phosphorus (figs. 8-13) vary throughout the basin. The median concentration of dissolved radium-226 is fairly stable (fig. 14). These variations are due to climate, geology, land-use, and water-use conditions. The northern part of the basin is high in altitude and mountainous. Rainfall and snowfall occur frequently and streams are perennial. Igneous, metamorphic, and sedimentary rocks outcrop here. The igneous and metamorphic rocks generally are less porous, less permeable, and more resistant to erosion. Runoff from this surface geology contains small concentrations of dissolved solids. In the southern part of the basin, altitudes are lower and the topography is dominated by mesas, hogbacks, washes, draws, canyons, badlands, and sand dunes. Rainfall and snowfall are sparse and streamflow is ephemeral. Sedimentary shales and sandstones are the predominant geologic deposits, and the land is sparsely vegetated. Runoff from this part of the basin generally contains larger concentrations of dissolved solids than runoff from the northern part of the basin. A criterion was chosen to determine the ability of the NASQAN stations (San Juan River at Shiprock and Animas River at Farmington) to represent water quality at selected upstream stations. If the mean, median, and mode of a constituent in tables 2 through 11 were within plus or minus 25 percent of the same constituent's value at the downstream NASQAN station, then the NASQAN station was judged to be representative of the upstream station. Trends detected at the selected stations are shown in figure 44 and listed in table 16 for comparison with trends detected at the NASQAN stations. The NASQAN stations do not represent water quality at other specific points throughout the basin. No single station could represent water quality throughout this basin. The climate, geology, and land use are not uniform, and these conditions affect water-quality variation. The NASQAN stations represent water quality at the station site. In the case of NASQAN station 09368000, San Juan River at Shiprock, New Mexico, the station represents the integration of water quality from the entire upstream basin. This integration of water quality is important. Assume that there is a persistent and large-load, water-quality change upstream; the change will also occur at the NASQAN site. The NASQAN-site water-quality analysis would signal an observer that conditions have changed somewhere in the basin upstream of the NASQAN site. The observer may want more detailed information on the change and may do some upstream sampling to determine the origin of the change. 77 If the upstream water-quality change was not persistent or large in load, then the NASQAN station would not accurately reflect that change. Situations in which an upstream change in water quality would not also occur at the NASQAN site would be the following: (1) The change occurring upstream is transitory in nature and has stabilized to downstream conditions within the upstream-to-downstream travel time; (2) the change occurring upstream is a one-time or infrequent occurrence and the sampling time at the downstream station does not correspond with the time when the affected water is passing by; and (3) the change occurring upstream involves a small volume of streamflow and is diluted to the point of being unnoticeable at the downstream site. The NASQAN station's data provide accurate information on how much water quality is changing over time. The information can be used to judge whether water quality is deteriorating, remaining the same, or improving. However, this is true only for water quality at the NASQAN site. The NASQAN station cannot accurately reflect what is occurring simultaneously in the remainder of the basin. Again, it is an integration of the entire basin. When a change occurring upstream is persistent and involves a large volume of streamflow, the change also will be detected downstream at the NASQAN site. A water-quality, streamflow model would be necessary to accurately reflect what is occurring simultaneously at any point in the entire basin. The NASQAN station's data would provide the control data needed to calibrate and verify the model's results. Stations at the mouths of all tributaries and at selected locations perhaps every 20 to 30 miles along the main stem would need to be sampled frequently during approximately a 72-hour period for different streamflow and seasonal conditions. Present sampling at the NASQAN station could be supplemented with simultaneous sampling at tributaries and selected sites along the main stem over about a 72-hour period. A different streamflow and seasonal condition needs to be selected for sampling each year. In order to define any changes in the seasonal variation of water quality, monthly or more frequent sampling of specific conductance needs to be continued at the NASQAN stations. Quarterly to bimonthly sampling is desirable for other constituents. Water quality that has been well defined at a few stations would be preferred to water quality that has been poorly defined at many stations. 78 108' 109 107 38C EXPLANATI ON 16936800 U.S. GEOLOGICAL SURVEY GAGING 1 ' STATION AND NUMBER Box around number indicates a NASQAN station PARAMETER Arrow shows increasing or decreasing (|) trend. Circle indi cates the mean, median, and mode are within 25 percent of parameter value GRAN 3E of the nearest downstream NASQAN sta tion. POA, dissolved-orthophosphate phosphorus; Fe, dissolved iron; Na, dissolved sodium; Ra-226, dissolved radium-226; ss, suspended sediment; SC, specific conductance 40 KlLOMETERS Figure 44.--Trends in water-quality parameters at selected U.S. Geological Survey stations and ability of the NASQAN stations to represent water quality at upstream stations. 79 Table 16. Trends detected and a criterion describing the adequacy of NASQAN stations to represent water quality at selected stations in the San Juan River basin upstream from Shiprock, New Mexico Mean, median, and mode of the parameter tested are within 25 percent of the parameter value at the Station Parameter Trend downstream NASQAN number tested detected station 09342500 Specific conductance None No Dissolved sodium Dissolved sulfate Dissolved iron Dissolved manganese Dissolved-orthophosphate phosphorus Dissolved radium-226 PH Streamflow None No Suspended sediment 09346000 Specific conductance None No Dissolved sodium None No Dissolved sulfate None No Dissolved iron None No Dissolved manganese Dissolved-orthophosphate None No phosphorus Dissolved radium-226 pH None Yes Streamflow None No Suspended sediment None No 09349800 Specific conductance None No Dissolved sodium Dissolved sulfate Dissolved iron Dissolved manganese Dissolved-orthophosphate phosphorus Dissolved radium-226 pH Streamflow None No Suspended sediment 80 Table 16. Trends detected and a criterion describing the adequacy of NASQAN stations to represent water quality at ^elected stations in the San Juan River basin upstream from Shiprock, New Mexico - Continued Mean, median, and mode of the parameter tested are within 25 percent of the parameter value at the Station Parameter Trend downstream NASQAN number tested detected station 09352900 Specific conductance None No Dissolved sodium None No Dissolved sulfate None No Dissolved iron None No Dissolved manganese None No Dissolved-orthophosphate None No phosphorus Dissolved radium-226 None Yes pH Decrease No Streamflow None No Suspended sediment Increase No 09355500 Specific conductance None No Dissolved sodium None No Dissolved sulfate None No Dissolved iron None Yes Dissolved manganese None No Dissolved-orthophosphate None No phosphorus Dissolved radium-226 None No pH None No Streamflow None No Suspended sediment None No 09356565 Specific conductance None No Dissolved sodium None No Dissolved sulfate None No Dissolved iron Increase No Dissolved manganese None No Dissolved-orthophosphate phosphorus Dissolved radium-226 None No pH None No Streamflow None No Suspended sediment None No 81 Table 16 Trends detected and a criteriondescribing the adequacy of NASQAN stations to represent water quality at gjelecjEed^s tat ions in the San Juan River basin upstream from Shiprock, New Mexico - Continued Mean, median, and mode of the parameter tested are within 25 percent of the parameter value at the Station Parameter Trend downstream NASQAN number tested detected station 09357500 Specific conductance None No Dissolved sodium None No Dissolved sulfate None No Dissolved iron None No Dissolved manganese None No Dissolved-orthophosphate None Yes phosphorus Dissolved radium-226 pH None No Streamflow None No Suspended sediment None No 09364500 Specific conductance None NASQAN Dissolved sodium None Station Dissolved sulfate None Dissolved iron None Dissolved manganese None Dissolved-orthophosphate None phosphorus Dissolved radium-226 None pH None Streamflow None Suspended sediment Decrease 09366500 Specific conductance None No Dissolved sodium None Yes Dissolved sulfate Increase No Dissolved iron None No Dissolved manganese None No Dissolved-orthophosphate phosphorus Dissolved radium-226 pH None Yes Streamflow None No Suspended sediment None No 82 Table 16. Trends detected and a criterion describing the adequacy of NASQAN stations to represent water quality at j?elected_s tatiqns^ in Jthe San Juan^ Riyer^ bag in ups tream from Shiprock, New Mexico - Concluded Mean, median, and mode of the parameter tested are within 25 percent of the parameter value at the Station Parameter Trend downstream NASQAN number tested detected station 09367950 Specific conductance Decrease No Dissolved sodium Decrease No Dissolved sulfate Decrease No Dissolved iron None No Dissolved manganese None No Dissolved-orthophosphate None No phosphorus Dissolved radium-226 None No pH None No Streamflow None No Suspended sediment None No 09368000 Specific conductance None NASQAN Dissolved sodium None Station Dissolved sulfate None Dissolved iron None Dissolved manganese None Dissolved-orthophosphate None phosphorus Dissolved radium-226 None pH None Streamflow None Suspended sediment None 09367561 Specific conductance Increase No Dissolved sodium Increase No Dissolved sulfate Increase No Dissolved iron Increase No Dissolved manganese None No Dissolved-orthophosphate None No phosphorus Dissolved radium-226 None No pH Decrease No Streamflow None No Suspended sediment None No 83 NEED FOR FUTURE STUDY Topics of interest for continued study are enumerated as follows: (1) Exploratory data analysis of sampling frequency For water-quality constituents collected monthly or more frequently, a monthly, bimonthly, and quarterly subset of the original data set can be used to determine annual concentrations and loads, which will provide a comparison of the influence of data-collection frequency on the determination of annual concentrations and loads. (2) Correlation of NASQAN stations with upstream stations Water- quality concentrations and loads at the NASQAN stations can be plotted on one axis against upstream water-quality concentrations and loads on the other axis to determine if mathematical relations exist; if a good relation exists, even though the NASQAN station does not represent water quality at the upstream station, it could be used to predict water quality at the upstream station after the proper mathematical relation is applied. (3) Flow-adjusted concentration-Seasonal Kendall test for trend magnitude Water-quality-constituent concentrations can be adjusted for flow and then tested by the Seasonal Kendall test to determine if a significant trend exists and if so, its magnitude; this result can be compared with the unadjusted trend results to determine if the flow-adjustment procedure gives different results. 84 SUMMARY OF RESULTS The Accounting Unit 140801, upstream from NASQAN site 09368000, is the San Juan River drainage basin upstream from Shiprock, New Mexico. The San Juan River drainage basin upstream from Shiprock includes high mountain cobble streams in the north and ephemeral sand channels in the south. The San Juan River is the second largest tributary of the Colorado River. Water-quality data from the U.S. Geological Survey WATSTORE files and the New Mexico Environmental Improvement Division's files were analyzed. The analyses were made to describe water-quality variability in streams on both a spatial and temporal basis; to relate water-quality variability to general causes; and to determine whether water-quality data collected at NASQAN stations, San Juan River at Shiprock (09368000) and Animas River at Farmington (09364500), are representative of water quality in the upstream drainage basin. Streamflow (0.00 to 13,700 cubic feet per second), specific conductance (30 to 16,300 microsiemens per centimeter at 25 °Celsius), pH (2.4 to 10.4 units), dissolved-sodium concentration (0.1 to 3,700 milligrams per liter), dissolved-sulfate concentration (1.7 to 8,300 milligrams per liter), dissolved-iron concentration (0 to 21,000 micrograms per liter), dissolved- manganese concentration (0 to 8,800 micrograms per liter), and suspended- sediment concentration (0 to 966,000 milligrams per liter) are the most variable properties and constituents. Dissolved-orthophosphate phosphorus concentration (0.00 to 2.6 milligrams per liter) and dissolved-radium-226 concentration (0.02 to 0.56 picocurie per liter) are much less variable. Most streams in the northeastern part of the basin have calcium bicarbonate waters (fig. 7 and table 12). Streams in the northwestern and southern part of the basin have calcium sulfate and sodium sulfate waters. Geology, climate, and land use affect the water quality and consequently, the water-quality classification. In those parts of the study area at high altitudes, much of the precipitation is in the form of snow. Streamflow from snowmelt runoff in this area has largely calcium bicarbonate water. Metals mining may contribute a sulfate component to Streamflow in the parts of the basin where the mines are located. Irrigation-return flow likely contributes a sodium component to Streamflow in some parts of the basin. Porous sandstones and interbedded shales in the southern part of the basin yield runoff with large dissolved-solids concentration. The San Juan River at Shiprock, NASQAN station 09368000, shows a water-quality classification resulting from integration of the many tributaries feeding the San Juan River. Streamflow at this station contains a calcium sulfate water 53 percent of the time and a calcium sodium sulfate water 27 percent of the time. The station does not reflect the variety of water-quality classifications at upstream tributaries or the water-quality classification existing at upstream tributaries for a chosen point in time. However, it does represent the integration of upstream waters and the outflow to downstream sites. 85 Median concentrations of water-quality constituents plotted at selected stations throughout the basin (figs. 8-14) show a range for specific conductance of 50 to 6,570 microsieraens per centimeter; dissolved sodium, 1.1 to 1,300 milligrams per liter; dissolved sulfate, 4.3 to 3,800 milligrams per liter; dissolved iron, less than 10 to 410 micrograms per liter; dissolved manganese, less than 10 to 430 micrograms per liter; dissolved-orthophosphate phosphorus, less than 0.01 to .08 milligram per liter; dissolved radium-226, .06 to .10 picocurie per liter. Specific-conductance, sodium, and sulfate variation is similar throughout the basin. The smallest values are reported from stations in the northeastern mountainous areas where snowmelt contributes largely to streamflow. Largest values are located downstream from power- generation facilities. Other fairly large values in the southern part of the basin are influenced by the ground-water-flow component of the streamflow. Irrigation-return flow increases values in the central part of the basin. Dissolved-iron concentration is greatest in the southern part of the basin and may be due in part to dissolution of iron minerals from soils and rocks in that area. Some large concentrations of dissolved manganese are associated with the metals-mining area in the northern tip of the basin. Dissolved- orthophosphate phosphorus and radium-226 concentrations appear to be fairly uniform throughout the basin. The product of specific conductance and streamflow (fig. 15) indicates that samples taken monthly or less frequently may result in an overestimation of loads. About one-third of the specific-conductance-streamflow product calculated for the drainage basin originates upstream of, Archuleta, which is 25 percent of the total basin area; one-third originates in the Animas River basin, which is 10.5 percent of the total basin area; one-eighth originates from the Canon Largo and La Plata and Chaco River basins, which are 51.5 percent of the total basin area; and about one-fifth cannot be accounted for and is assumed to originate from small ungaged drainages or to flow to the main stem as unidentified sources between the gaging stations at Archuleta and Shiprock (table 13). Based on box-and-whisker plots, streamflow has the greatest number of far-out values at individual stations. From station to station, streamflow is also highly variable and influences water-quality constituents through dilution. Dissolved-iron and suspended-sediment concentrations are the water- quality constituents with the largest number of far-out values. The central values for dissolved iron are fairly uniform from station to station within the basin. Suspended sediment is much more variable among stations. Dissolved radium-226 is the constituent with the least number of far-out and outside values. It also does not vary greatly from station to station. Specific conductance, pH, dissolved-orthophosphate phosphorus, dissolved sodium, dissolved sulfate, and dissolved manganese fall somewhere between in variability at a single station. Central values of specific conductance and sulfate are the most variable from station to station of this group of properties and constituents. 86 The wastewater from one of the power-generation facilities in the drainage basin has the greatest water-quality variability of all stations for most constituents. It also contributes the largest concentrations of these constituents to the stream system. Small quantities of flow from the Ca'non Largo tributary (station 09356565) add large concentrations of dissolved sodium, dissolved sulfate, dissolved manganese, and suspended sediment to the stream system. This tributary also contributes water with large specific conductance to the stream system. The small to ephemeral flows at stations in the southern part of the drainage basin have the most variable water quality and commonly have large constituent concentrations. These stations have little influence on water quality in the San Juan River main stem, but they are representative of conditions in the southern part of the basin. The two NASQAN stations have large volumes of streamflow and generally are among the lowest in variability within the study area. A trend in water quality was detected at 14 out of 36 stations tested (table 15). The time period for trend testing was October 1, 1973, through September 30, 1981. Of those 14 stations, 5 are downstream from point-source discharges from power-generation facilities. Water-quality measurements taken at these stations may be reflecting changes in coal- or power-production rates over the years and changes in water-discharge practices. At other stations in the study area, one showed an increase in suspended sediment, one a decrease in suspended sediment, one an increase in dissolved iron, one a decrease in dissolved iron, three a decrease in pH, one an increase in dissolved- orthophosphate phosphorus, one an increase in dissolved sulfate, and one a decrease in specific conductance and dissolved sodium. At the upstream NASQAN station, Animas River at Farmington, a decrease in suspended-sediment concentration of 78 milligrams per liter per year was detected. At the downstream NASQAN station, San Juan River at Shiprock, no trends were detected. At the stations upstream from San Juan River at Shiprock, there were both increasing and decreasing trends for several constituents, which might cancel each other. The most consistent trend in the basin was the decrease in pH at six stations, three of which are downstream from coal-mine and power-generation activities. Hydrographs commonly showed seasonal variation in water quality (figs. 33-43). At stations 09367950, FC1, and FC3, monotonic trends are apparent. These stations are associated with point-source discharges of wastewater and represent changes in the wastewater rather than in the natural streamflow. At station 09357100 a step decrease in specific conductance occurred between October 1, 1978, and October 1, 1979 (fig. 34). The hydrographs at the two NASQAN stations, San Juan River at Shiprock and Animas River at Farmington, show correspondence, particularly for periods of small concentrations, for the property of specific conductance and constituents of dissolved sodium and dissolved sulfate. 87 Water quality is variable throughout the San Juan River basin upstream from Shiprock, New Mexico, due to climatic, geologic, land-use and water-use conditions within the study area. The NASQAN stations represent water quality at the station site, not what is occurring simultaneously elsewhere in the basin. The NASQAN stations have large volumes of flow, which represents an integration of the flow from many upstream tributaries. The NASQAN data provide accurate information on how water quality is changing over time. If a change occurring upstream is persistent and involves a large volume of streamflow, it likely will also be detected at the downstream NASQAN station. A water-quality, streamflow model would be necessary to accurately reflect what is simultaneously occurring in the entire basin. Present sampling at the NASQAN stations could be supplemented with simultaneous sampling over the upstream drainage basin that would be suitable for input into a model. Sample frequency needs to be maintained in order to preserve definition of the seasonal variation. Water quality that has been well defined at a few stations would be preferred to water quality that has been poorly defined at many stations. 88 SELECTED REFERENCES Colorado Water Conservation Board and U.S. Department of Agriculture, 1974, Water and related land resources, San Juan River basin, Arizona, Colorado, New Mexico, and Utah: Denver, Colo., Water Conservation Board, p. IV-6 to IV-7. Crawford, C.G., Slack J.R., and Hirsch, R.M., 1983, Nonparametric tests for trends in water-quality data using the statistical analysis system: U.S. Geological Survey Open-File Report 83-550, 102 p. Dane, C.H., and Bachman, G.O., 1965, Geologic map of New Mexico: U.S. Geological Survey, scale 1:500,000, 2 sheets. Gerig, T.M., 1980, The SPLOT procedure, in SAS supplemental library user's guide, 1980 edition: Raleigh, N. C., SAS Institute Inc., p. 173-175. Hem, J.D., 1970, Study and interpretation of the chemical characteristics of natural water: U.S. Geological Survey Water-Supply Paper 1473, 363 p. Miller, C.R., 1951, Analysis of flow duration sediment rating curve method of computing sediment yield: U.S. Bureau of Reclamation Report, 55 p. Nielsen, G.F., editor-in-chief, 1982, Keystone Coal Industry Manual 1982: New York, McGraw-Hill, 1466 p. Roybal, F.E., and others, 1983, Hydrology of Area 60, northern Great Plains, and Rocky Mountain coal provinces, New Mexico, Colorado, Utah and Arizona: U.S. Geological Survey Open-File Report 83-203, p. 42. Sorenson, E.F., 1967, San Juan River basin: settlement, development, and water use, in Water resources of New Mexico; occurrence, development, and use: New Mexico State Planning Office, p. 198-210. Tukey, J.N., 1977, Exploratory data analysis: Reading, Mass., Addison-Wesley Publishing Co., 506 p. Tweto, Ogden, compiler, 1979, Geologic map of Colorado: U.S. Geological Survey, scale 1:500,000, 2 sheets. U.S. Department of Commerce, Bureau of the Census, 1860-1980, Population and agricultural statistics for the years 1860-1980: U.S. Government Printing Office (published yearly). Younger, M.S., 1979, Handbook for linear regression: Belmont, Calif., Wadsworth, Inc., 569 p. 89 U.S. GOVERNMENT PRINTING OFFICE:1987- 775-651/65163